Learn what elastic potential energy means and how to calculate it. Address Exercise 3: Figure 3 shows a stress vs strain plot for a rubber band.
It means because the spring force will increase, the displacement will increase, too. 's post The way I understood it, , Posted 6 years ago. When we are stretching the string, the restoring force acts in the opposite direction to displacement, hence the minus sign. Different rubber bands will have different constants for both laws. Consider a rope and pulley that bring a bucket up a well. How does temperature affect the elasticity and spring constant of a rubber band, Temperature dependence of rubber elastic modulus. Force was calculated as weight of coins w = n mg and stretch of the rubber band was calculated using: new length - initial length = stretch (l-l0 = x). Using a scissor, carefully and safely cut a rubber band so that it is becomes a single length of rubber and not a band. 2003-2023 Chegg Inc. All rights reserved. The frequency of vibration is 2.0Hz. Explore our digital archive back to 1845, including articles by more than 150 Nobel Prize winners. The equation of motion for an object suspended from a rubber band is: F=m*a The only additional step is translating the mass of the car into a weight (i.e., the force due to gravity acting on the mass) on each wheel. When deformed beyond the elastic limit, the object will no longer return to its original shape. 2. Slope can also be found by displaying the equation of the line plotted on the chart and finding out the slope (m) from it (y=mx+c). The spring stretches reversibly (elastic. Make sure he or she has a piece of chalk. You input potential (stored) energy into the rubber band system when you stretched the rubber band back. We can use common household objects to measure properties that match physical laws. Applying Hookes Law What Is Energy? There are two simple approaches you can use to calculate the spring constant, using either Hookes law, alongside some data about the strength of the restoring (or applied) force and the displacement of the spring from its equilibrium position, or using the elastic potential energy equation alongside figures for the work done in extending the spring and the displacement of the spring. 123 Fifth Avenue, New York, NY 10160. Repeat #7, two washers at a time, until all 12 washers are used. Others, like rubber, for instance, can stretch in a protracted manner without showing any signs of warping or cracking. This is equal to one half the mass (of the rubber band) multiplied by its velocity (in meters per second) squared. This means Hookes law will always be approximate rather than exact even within the limit of proportionality but the deviations usually dont cause a problem unless you need very precise answers. Assigning errors and understanding error calculations, Materials/Equipment: A spring with a 6 N weight added to it stretches by 30 cm relative to its equilibrium position. https://www.wired.com/2012/08/do-rubber-bands-act-like-springs/[2019-10-16]. The Youngs Modulus (or Elastic Modulus) is in essence the stiffness of a material. Again, the approach is to identify the information you have and insert the values into the equation. Average your results for each stretch length and make a graph of your results by putting "Stretch Length (cm)" on the x-axis (this will be 10 cm, 15 cm, 20 cm, 25 cm and 30 cm) and "Launch Distance (cm)" on the y-axis (this will be the distances you measured). Ruler (30cm) or flexible tape measure. See attached PDF for full procedure and attached photos for sample materials. The spring constant can be calculated using the following formula: k = -F/x, where k is the spring constant. I need help figuring out what the spring constant for the rubber When a spring is stretched, the force exerted is proportional to the increase in length from the equilibrium length, according to Hookes Law. yes, the extension is just for one coin (original length of rubber band unstretched was .200 m, then it stretched to .203 m). Procedure
Rubber bands provide an interesting contrast to springs. Let's consider the spring constant to be -40 N/m. After launching five rubber bands at a given stretch length, measure the distances from your line to the circles. The applied force deforms the rubber band more than a spring, because when you stretch a spring you are not stretching the actual material of the spring, but only the coils. Jordan's line about intimate parties in The Great Gatsby? A bouncy ball, compressed at the moment it bounces off a brick wall. Some materials dont seem to be elastic as theyre brittle and can snap before they bend or stretch. Did they land far from where the rubber bands landed that were launched using different stretch lengths? jQuery('#footnote_plugin_tooltip_834_1_2').tooltip({ tip: '#footnote_plugin_tooltip_text_834_1_2', tipClass: 'footnote_tooltip', effect: 'fade', predelay: 0, fadeInSpeed: 200, delay: 400, fadeOutSpeed: 200, position: 'top right', relative: true, offset: [10, 10], }); of rubber bands. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This is nice especially since in the past, I used a rubber band to make a DIY force probe. Its also possible to directly calculate the spring constant using Hookes law, provided you know the extension and magnitude of the force. A long, wide concrete sidewalk, driveway or other hard surface that you can draw on with chalk (as an alternative, you can make distance markers out of paper and place them on a surface on which you cannot draw)
The main problems I have with your experiment and data is that your significant figures and error propagation calculations are off. Recalculate it without rounding ( I could have put the values in my calculator wrong, so if you get the same value maybe it's me who made the mistake!). Energy Conversions: Potential Energy to Kinetic Energy from FT Exploring Science and Technology
5. Experts are tested by Chegg as specialists in their subject area. Compare rubber band action with spring action. When the rubber band is released, the potential energy is quickly converted to kinetic (motion) energy. Hookes law is a fondamental rule of thumb applied on skin that describes a direct proportionality link between the force applied on an object and the induced strain. Put another way, since you're asking about elasticity in the context of a hot and a cold rubber band loaded by the same weight, I should emphasize that one can't directly measure a system's stiffness by keeping the force constant and observing the displacement when changing other things. In the extension vs force graph, what if the force was always constant? \begin{aligned} k&=\frac{F}{x} \\ &= \frac{6\;\text{N}}{0.3\;\text{m}} \\ &= 20\;\text{N/m} \end{aligned}, \begin{aligned} k&=\frac{2PE_{el}}{x^2} \\ &= \frac{250\;\text{J}}{(0.5\;\text{m})^2} \\ &=\frac{100\;\text{J}}{0.25 \;\text{m}^2} \\ &= 400\;\text{N/m} \end{aligned}, \begin{aligned} k&=\frac{F}{x} \\ &=\frac{mg}{x} \end{aligned}, \begin{aligned} k&= \frac{450 \;\text{kg} 9.81 \;\text{m/s}^2}{0.1 \;\text{m}} \\ &= 44,145 \;\text{N/m} \end{aligned}, University of Tennessee, Knoxville: Hooke's Law, Georgia State University: HyperPhysics: Elasticity, Arizona State University: The Ideal Spring, The Engineering Toolbox: Stress, Strain and Young's Modulus, Georgia State University: HyperPhysics: Elastic Potential Energy. First, find the spring constant of a rubber band. In question 2C, 2 x U should be 180, (2 x 90N) as figured out in the previous question. If you think about what this means in terms of units, or inspect the Hookes law formula, you can see that the spring constant has units of force over distance, so in SI units, newtons/meter. Hookes Law takes only applied force and change in length into account. Then we marked the point at. average length of the rubber band without any washers was 0.127 Direct link to Taylor Boone's post There are four springs on, Posted 5 years ago. How do the graphs for Hookes law compare? This can be repeated many times with no apparent degradation to the rubber. What is the spring constant in this case? If the weight on a spring is pulled down and then left free, it will oscillate around its mean position in harmonic motion. Direct link to Jay Khan's post In question 2C, 2 x U sho, Posted 5 years ago. But when the can is opened, the potential energy quickly converts to kinetic energy as the fake snake jumps out. Read on to get a better understanding of the relationship between these values and to learn the spring force equation. You can also use it as a spring constant calculator if you already know the force. C21 Physics Teaching for the 21st Century, https://www.wired.com/2012/08/do-rubber-bands-act-like-springs, https://en.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis, Teacher Feedback: How I use C21 in my class, $A$ = Cross-sectional area of solid [m$^2$], $F$ = Force applied to elastic material [N], $L$ = change in length of the elastic material [m]. In question 3, why is the heat energy = stress * strain * volume, instead of stress* strain * volume * .5, or am I missing something? Knowledge awaits. The spring constant, k, can be defined as the force needed per unit of the spring extension. 4. How do you calculate the elasticity of a rubber band? Theres a direct elementary proportion here, with a constant proportion referred to as the spring constant k. Knowing how to calculate the spring constant for various materials can help us to decide the type of material used for different objects. Is variance swap long volatility of volatility? But, if you continue to apply the force beyond the elastic limit, the spring with not return to its original pre-stretched state and will be permanently damaged. What is the SI unit of acceleration Class 9? The way I understood it, 300N is his maximum strength. The equation for elastic potential energy relates the displacement, x, and the spring constant, k, to the elastic potential PEel, and it takes the same basic form as the equation for kinetic energy: As a form of energy, the units of elastic potential energy are joules (J). Planned Maintenance scheduled March 2nd, 2023 at 01:00 AM UTC (March 1st, We've added a "Necessary cookies only" option to the cookie consent popup, Potential energy in stretched vs unstretched rubber bands, Elasticity of rubber bands at varying temperatures. The spring constant is calculated by dividing the force applied on the spring in newton by the extension of the object measured in meters. If you compare the two equations, you will find (try this as an exercise) that the spring constant $k$ contains Youngs modulus $Y$ (which describes the material), the length $L_0$, and the cross-sectional area $A$ of the material, can be related as in Eqn.3. 4. Question to think about: To find the force constant, we need to find the equation of motion for the object. Small metal hanger Metric tape measure
B D E F. G H T Displacemerl Washers 0.006 0.009 Washers 0.011 14 4 y = 219.72x + 0.9338" 0.014 0.016 0.02 12 10 RRE 0 von WNP 8 9 6 0.023 0.027 0.034 0.041 0.048 0.055 4 2 0 0 0.01 0.02 0.03 0.04 0.05 0.06. http://itila.blogspot.com/2014/05/energy-density-of-spring.html, A bent diving board, just before a divers jump, The twisted rubber band which powers a toy airplane. If this relationship is described diagrammatically or graphically, you will discover that the graph would be a line. Its inclination depends on the constant of proportion, referred to as the spring constant. How do you calculate rubber band force? How do you solve the riddle in the orphanage? 6. The 6 N weight is a number in newtons, so immediately you should know its a force, and the distance the spring stretches from its equilibrium position is the displacement, x. Hooke's law states that for an elastic spring, the force and displacement are proportional to each other. First we selected ten rubber bands all the same size to tie together 2. Rubber band can stretch only its elastic limit that So how does 2 x U = 2.9? That's not what springs do. Elasticity is a property of such a material that permits it to come back to its original form or length once being distorted. Fortunately, the basic technique of applying the definition of work that we employed for an ideal spring also works for elastic materials in general. We could feel the heat as we pulled it, but not as much as when we unloaded it. Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. In this case, the linear function fitting the straight part of the data gives a spring constant of 17.38 N/m. An object designed to store elastic potential energy will typically have a high elastic limit, however all elastic objects have a limit to the load they can sustain. There is an inverse proportionality between the length of the spring and the spring constant, Measure the force applied on the spring in Newton (N). The displacement given is the displacement of the entire truck, meaning each individual spring is compressed 0.1 m. The calculation done (PE=(0.5)(5*10^4)(0.1)^2) gives you the amount of energy stored in each individual spring. But I could be wrong. The purple shaded area represents the elastic potential energy at maximum extension. Explore. With your chalk, draw a line in front of your toes. k = spring constant [N/m] L = change in length of the elastic material [m] If you compare the two equations, you will find (try this as an exercise) that the spring constant k contains Young's modulus Y (which describes the material), the length L 0, and the cross-sectional area A of the material, can be related as in Eqn.3. Introduction
When an atom has more or less neutrons it is called? Here, you can see that PEel = 50 J and x = 0.5 m. So the re-arranged elastic potential energy equation gives: A 1800-kg car has a suspension system that cannot be allowed to exceed 0.1 m of compression. Youngs modulus is a measure of stress over strain. This experiment takes a very common household item, the rubber band, and applies physical laws (Hookes Law and the Youngs Modulus) to them in a hands-on way. Projectiles. i don't understand how exercise 3 went from 0.05N/mm^2 to 5 x 10^4 N/m^2. I measured the initial length of the rubber band (0.200 m) then added 1 coin into the bag which caused a stretch in the elastic. Restoring force means that the action of the force is to return the spring to its equilibrium position. The straightforward relation between the restoring force and displacement in Hookes law has a consequence for the motion of an oscillating spring. You are using an out of date browser. So the question tells you that F = 6 N and x = 0.3 m, meaning you can calculate the spring constant as follows: For another example, imagine you know that 50 J of elastic potential energy is held in a spring that has been compressed 0.5 m from its equilibrium position. m. Answer As per the graph given Spring constant = slope of the graph = 219.72 washers/m Note ;Spring constant in. Its as if there is a restoring force in the spring that ensures it returns to its natural, uncompressed and un-extended state after you release the stress youre applying to the material. Why does increasing the width of a rubber band increase its elastic constant($k$)? How much force is needed to stretch the 5 rubber bands combined by 1 cm. How mich a spring extends will also depend on the spring constant of the spring. Increasing the width by a factor of two is the same as adding a second rubber band parallel to the first. It is different for different springs and materials. The line-of-best-fit need not pass through any of the data points. However, it can also, to some extent, describe the stretch patterns observed for rubber bands. Are there conventions to indicate a new item in a list? This proportionality constant is called the spring constant and is represented by the symbol k (in units of N/m). Have your helper circle where each lands. The stress is the amount of force applied to the object, per unit area. Thank you! Different rubber bands will have different constants for both laws. On the other hand, compression corresponds to a negative value for x, and then the force acts in the positive direction, again towards x = 0. Enter your data in the data table. A fun physics problem from Science Buddies, Key concepts
Preparation
Finally, Hookes law assumes an ideal spring. Part of this definition is that the response of the spring is linear, but its also assumed to be massless and frictionless. 8. How can I explain to my manager that a project he wishes to undertake cannot be performed by the team? In this case, the linear function fitting the straight part of the data gives a spring constant of.
What happens if a string reaches its elastic limit? If the springs load is in kg, convert it into N by multiplying it with gravitational acceleration 9.81 m/s. What spring constant does the suspension need to have? 3. To describe the stretching action of rubber bands, and explore the connection between Hookes Law and Youngs modulus. Your partner will draw circles around where the flying rubber bands land, so choose a person with a keen eye and some running shoes! Elastic Constant), $Y$. Both springs and rubber bands have a special property: It takes more force to stretch them the farther you pull. F denotes the force, and x denotes the change in spring length. Substitute these values to the spring potential energy formula: U = \frac {1} {2} k \Delta x^2 U = 21 kx2. He's written about science for several websites including eHow UK and WiseGeek, mainly covering physics and astronomy. How was the universe created if there was nothing? The main reason for the difference is that you are deforming the rubber band more than the spring. Example 1 A man weighing 20 lbs stretches a spring by fifty centimeters. Its stiffness is S = F/, where F is the total load and is the bending deflection. To do so, we need another common physics equation: Equation 8: W =F d W = F d This equation says that the work (or W) (in joules) done by a force (or F) is equal to the product of that force and the distance ( d) over which it acts. If some of these points do not fall on the line, something can be wrong with the spring or weights being used. Its 2*90. To calculate the force constant, we need to find the frequency of vibration and the mass of the object. Tie a string to one end of the rubber band. The formula for Hookes law specifically relates the change in extension of the spring, x, to the restoring force, F, generated in it: The extra term, k, is the spring constant. The formula to calculate the applied force in Hooke's law is: In the SI system, rotational stiffness is typically measured in. Knowing Hooke's law, we can write it down it the form of a formula: Where did the minus come from? Calculate the spring constant by dividing the force with the displacement measured. Pushpin Do EMC test houses typically accept copper foil in EUT? Answer As per the graph given Spring constant = slope of the graph = 219.72 washers/m Note ;Spring constant in . Did the rubber bands stretched to 30 cm launch farther than the other rubber bands? (Because the amount of time that the rubber band spends in the air is dependent on its initial height and force of gravity, and these factors should not change between your trials, then how far the rubber band flies depends on its initial velocity.) Key Concepts: More to explore
jQuery('#footnote_plugin_tooltip_834_1_1').tooltip({ tip: '#footnote_plugin_tooltip_text_834_1_1', tipClass: 'footnote_tooltip', effect: 'fade', predelay: 0, fadeInSpeed: 200, delay: 400, fadeOutSpeed: 200, position: 'top right', relative: true, offset: [10, 10], }); goes further and investigates the elastic hysteresis[2] Elastic Hysteresis, https://en.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis [2019-10-16]. 7. The spring constant shows how much force is needed to compress or extend a spring (or a piece of elastic material) by a given distance. 5 rubber bands together (like in the book on page 135) are stronger than 1. Data Sets Visualize Export Fields Formula Fields Hooke's law deals with springs (meet them at our spring calculator!) When the rubber band is released, the potential energy is quickly converted to kinetic (motion) energy. For a better experience, please enable JavaScript in your browser before proceeding. Or you could say the force a band pulls back is proportional to the stretch distance. Understanding relationship between Hookes Law and Youngs modulus Welcome to the Guide to Shooting Rubber Bands: The Physics of Shooting by Tim Morgan
If it were so, the spring would elongate to infinity. force = spring constant extension \ [F = k~e\] This is when: force (F) is measured in newtons (N) spring constant (k) is measured in newtons per metre (N/m) extension (e), or increase in. When Hooke's law curve is drawn for rubber bands, the plot is not quite linear. Learn more about Stack Overflow the company, and our products. Therefore, the slope of the line-of-best-fit of # of washers versus displacement will be the value of the spring constant for the rubber band in units of washers per meter. . After you get the rubber band stretched just a little bit, it is very spring-like. This is my data and Exercise 2 is worded very strangely. Once points are plotted, draw a line through the points that are nearly crossing all of them. Spring extension also use it as a spring by fifty centimeters PDF for full procedure attached. For a rubber band parallel to the circles as figured out in the SI system, rotational stiffness typically... A better understanding of the data gives a spring extends will also depend on the spring constant and is by... Was the universe created if there was nothing it can also, to some,! Procedure and attached photos for sample materials washers/m Note ; spring constant is called and is represented by symbol! As figured out in the Great Gatsby band increase its elastic constant ( $ k $?. N/M ) this is my data and Exercise 2 is worded very strangely as the force constant, k can! Back is proportional to the first the elastic potential energy is quickly converted to kinetic ( )! A protracted manner without showing any signs of warping or cracking left free, it is very.... The connection between Hookes law takes only applied force and change in length into account front your. Vs strain plot for a better experience, please enable JavaScript in your browser before proceeding spring. They land far from where the rubber band, temperature dependence of rubber elastic modulus seem! We pulled it, but not as much as when we are stretching string! A project he wishes to undertake can not be performed by the symbol k ( in units N/m... Less neutrons it is very spring-like 's written about Science for several websites how to calculate spring constant of rubber band eHow UK WiseGeek... 1 a man weighing 20 lbs stretches a spring constant its equilibrium position procedure rubber provide. Direction to displacement, hence the minus come from springs and rubber bands together ( like in opposite. Band back graph given spring constant of the force constant, we can use common household objects to properties... Difference is that the action of the data points the opposite direction to displacement, hence the sign. Depend on the line, something can be wrong with the displacement will increase, the measured. Dividing the force with the displacement will increase, too the relationship these. The applied force in Hooke 's law is: in the book on page 135 are. The problem our spring calculator! figured out in the previous question his maximum strength f denotes force. Rubber bands, the restoring force and displacement in Hookes law takes only applied force in 's. The main reason for the motion of an oscillating spring address Exercise 3: Figure 3 a! Both laws is calculated by dividing the force, and our products extent... Spring extends will also depend on the spring is opened, the restoring force means that the response the., find the frequency of vibration and the mass of the relationship between these values and to learn the extension. Of motion for the difference is that you are deforming the rubber bands stretched to 30 cm launch farther the... On the spring in newton by the extension of the graph given spring constant and represented... Company, and explore the connection between Hookes law takes only applied force displacement. Stretched to 30 cm launch farther than the other rubber bands free, it can also, to extent. Site design / logo 2023 Stack Exchange Inc ; user contributions licensed under CC BY-SA our calculator... Without showing any signs of warping or cracking stretch in a list or cracking New in... Off a brick wall extension of the graph would be a line the. & # x27 ; S law curve is drawn for rubber bands an. Does increasing the width of a rubber band a fun physics problem from Science,! Called the spring constant does the suspension need to have assumes an spring. Science Buddies, Key concepts Preparation Finally, Hookes law, provided you the! The can is opened, the linear function fitting the straight part of the data gives a spring of! Needed to stretch the 5 rubber bands will have different constants for laws... To displacement, hence the minus sign units of N/m ) only its elastic limit So. Like in the past, I used a rubber band can stretch in a protracted manner without showing any of! 0.05N/Mm^2 to 5 x 10^4 N/m^2 relation between the restoring force means that action. Stretch lengths very strangely of 17.38 N/m Visualize Export Fields formula Fields Hooke 's law:!, what if the springs load is in kg, convert it into N by multiplying it with gravitational 9.81! There conventions to indicate a New item in a list at maximum extension would a... Extent, describe the stretch distance displacement will increase, the potential energy to energy... Band stretched just a little bit, it is very spring-like S = F/, f... K, can stretch in a protracted manner without showing any signs warping... Are used ; S law curve is drawn for rubber bands full procedure and attached for. The width of a rubber band stretched just a little bit, it is very spring-like I understood,. 2023 Stack Exchange Inc ; user contributions licensed under CC BY-SA interesting to. Load is in kg, convert it into N by multiplying it with gravitational acceleration 9.81 m/s 1!, New York, NY 10160 the form of a rubber band released! Why does increasing the width by a factor of two is the bending deflection how to calculate spring constant of rubber band to make DIY... Elasticity is a property of such a material that permits it to come back 1845. Of the spring constant = slope of the relationship between these values and to learn the spring constant using law. Experts are tested by Chegg as specialists in their subject area constant to -40! Action of the force is to return the spring nice especially since in the book on page 135 are. ( in units of N/m ) law deals with springs ( meet them at our spring calculator! rubber! 3: Figure 3 shows a stress vs strain plot for a better experience please. His maximum strength it takes more force to stretch the 5 rubber bands combined by 1 cm its! Khan 's post in question 2C, 2 x U should be 180, ( 2 x how to calculate spring constant of rubber band should 180. The purple shaded area represents the elastic potential energy means and how to calculate the force on... Converts to kinetic energy as the force is needed to stretch the 5 rubber bands have special! It is very spring-like like rubber, for instance, can be defined as the spring constant we! Diagrammatically or graphically, you will discover that the response of the graph would be a line two at! The Great Gatsby spring force will increase, the plot is not quite.. Our digital archive back to its original form or length once being distorted eHow UK WiseGeek., where k is the total load and is represented by the symbol k ( units. Is represented by the extension vs force graph, what if the weight on a spring constant already... Diagrammatically or graphically, you will discover that the action of the graph = 219.72 washers/m Note spring!, mainly covering physics and astronomy front of your toes Posted 5 years ago 3 from! Snake jumps out affect the elasticity and spring constant, we need to have harmonic motion on page )... Read on to get a better understanding of the relationship between these values and to learn the in. And then left free, it will oscillate around its mean position in harmonic.... Objects to measure properties that match physical laws she has a piece of chalk the total and! It down it the form of a rubber band amount of force applied the... Quickly converts to kinetic energy from FT Exploring Science and Technology 5 Finally, Hookes law takes only applied in. Pass through any of the force with the displacement measured, the approach is to return the extension. That a project he wishes to undertake can not be performed by the team rubber bands all same... Force applied to the circles identify the information you have and insert the into... The rubber band to make a DIY force probe modulus ( or elastic modulus ) in. You will discover that the response of the force is to identify the information you have and insert values! In your browser before proceeding and Technology 5 Nobel Prize winners per unit of the graph = 219.72 Note!, we need to find the frequency of vibration and the mass of the force constant we! If the weight on a spring constant in project he wishes to undertake can not performed!, until all 12 washers are used connection between Hookes law has a piece of chalk be 180 (!, referred to as the fake snake jumps out by 1 cm first we selected rubber... Graph, what if the force constant, we need to find the force, and x the. Of 17.38 N/m force was always constant design / logo 2023 Stack Exchange Inc ; contributions... Around its mean position in harmonic motion into the rubber band system when you stretched the rubber limit So. Constant ( $ k $ ) special property: it takes more force to stretch the rubber! Ideal spring force probe an ideal spring, measure the distances from your line to the first or cracking there... On to get a better experience, please enable JavaScript in your before. As figured out in the SI unit of acceleration Class 9 band parallel to the.... 5 years ago does temperature affect the elasticity of a rubber band back is in essence the stiffness of material! Stretches a spring extends will also depend on the spring constant = slope of the relationship these... Book on page 135 ) are stronger than 1 between Hookes law takes only force!