3 Force-Motion Online

P h y s i c s L a b ( O n l i n e S i m u l a t i o n ) FORCES AND MOTION: RAMP Mechanics TA name: Due Date: Student Name: Roman Dhimal Student ID: 1001800488 Simulation Activity #3: Forces and Motion: Ramp Simulation created by the Physics Education Technology Project (PhET) c/o The University of Colorado at Boulder http://phet.colorado.edu/ Link: http://phet.colorado.edu/en/simulation/ramp-forces-and-motion

P h y s i c s L a b ( O n l i n e S i m u l a t i o n ) Objective: This online activity is intended help you learn more about physics. We offer this lab in the hope that you will make connections between predictions and conclusions, concepts and actions, equations, and practical activities. Give this lab a chance! You will learn a lot, and you might even enjoy it! Answer all the questions as you follow the procedure and run the simulation. Familiarize yourself with the Ramp: Forces and Motion simulation using different scenarios as shown in the figures above. Click a tab at the top to view a scenario. For example, click the Introduction tab. Here, you can select an object from the drop-down menu at the center bottom. You can also drag the object or insert values in the spaces provided to move the box. Click the friction tab. You can now change more properties. If you like, you can change gravity using the sliding bar just below the object mass. Click the Force Graphs tab. You can observe graphs which represent what you are doing on the box. Take some time, and familiarize yourself with the controls. Once you understand how to run the simulation, you can predict the results based on the theoretical background (that is, the basics explained in the introduction below) and verify your calculations using the simulation. Introduction: When an object is dragged across a surface, the force of friction depends on the normal force ( 𝐹 ? ) and the coefficient of friction (  ). Depending on the situation, the normal force can be expressed in different ways. For example, if the force applied is parallel to the surface as shown below, the normal force is equal to the weight. If the surface is inclined, the normal force is equal to the weight times the cosine of the angle of the incline. Note that the friction changes as the normal force expression changes. If the box moves with constant velocity, the net force is zero. Note the general equation and the subsequent two equations in relation to the state of motion described and figure below: 1. 𝐹 ? = 𝜇𝐹 ? 2. Horizontal Surface: 𝐹 ? = 𝜇𝑚𝑔 3. Inclined Surface: 𝐹 ? = 𝜇𝑚𝑔 cos 𝜃   F n F n F f F app mg mg F f

P h y s i c s L a b ( O n l i n e S i m u l a t i o n ) i. Keeping the angle at 30 degrees, find the static and kinetic coefficients of friction Kinetic: 0.5 Static: 0.5-1.0 ii. Keeping the static and kinetic coefficients of friction to 0.4 and 0.3, find the ramp angle 21.9 degree e. Repeat steps a through d for an object on the moon. Did you find a different answer? Explain. - The answers were the same since the kinetic and static forces of friction were the same for steps a-d 3. Click Force graphs tab a. Check the 𝐹 ??𝑖𝑐?𝑖?? , 𝐹 ??𝑎?𝑖?𝑦 , and 𝐹 ??? boxes. b. Using the steps a,b,and c of procedure 1, and the ramp angle found in step d, run the simulation. c. What are the values of forces you read from the graphs i. On inclined plane: F Friction =_ 429.6 _____N, F Gravity =_ -429.6 _____N, F Sum =_ _0 ____N ii. On a horizontal suface: F Friction =_ 0__ __N, F Gravity =__ 0_ ___N, F Sum =_ 0_ ____N d. Repeat c using the setups a and b of procedure 2. i. On inclined plane: F Friction =_ 254.6 _____N, F Gravity =_ -490_ ____N, F Sum =__ - 235.4 ____N ii. On a horizontal suface: F Friction =_ _294_ ___N, F Gravity =_ _0_ ___N, F Sum =_ _294_ ___N iii. Using distances along the inclined plane and horizontal planes and the respective times from the graph, calculate the average speeds of the crate 1. on the inclined plane: v avg =_ 3.019_ _____m/s 2. on the horizontal surface: v avg =_ _2.977_ ____m/s e. Adjust the ramp angle to 30 degree, select sleepy dog, and run the simulation with wood then with ice using the friction control. Using the time information from the graph, and acceleration along the inclined plane, find the speed at the bottom of the inclined plane i. Wood: v=__ 3.282 ___m/s, Ice: v= _8.82_ ___m/s Follow up Questions: 1. As the angle of the ramp is increased, the normal force (increases / decreases / remains the same) and the friction force ( increases /decreases / remains the same) 2. As the angle of the ramp is increased, the parallel force (increases /decreases / remains the same). 3. The angle at which the force of gravity down the plane was equal to the force of friction (for the cabinet) was __ 26.5_ __________.

P h y s i c s L a b ( O n l i n e S i m u l a t i o n ) 4. Consider a very low (zero) friction, 5.0 kg skateboard on a ramp at an angle of 15° to the horizontal. What would be the net force that would cause acceleration when the skateboard is allowed to move? __ _12.68_ _________ N 5. What would the skateboa rd’s acceleration down the plane? _ ___2.54__ _______ m/s 2 6. Now consider the same no-friction 5.0 kg skateboard on the same 15 o ramp. If a 45kg teenager jumps on, what would be her acceleration down the ramp? __ __2.54_ ______ m/s 2 7. Imagine you are pushing a 15 kg cart full of 25 kg of bottled water up a 10 o ramp. If the coefficient of friction is 0.02, what is the friction force you must overcome to push the cart up the ramp? ___ _7.72__ _______ 8. Realizing that there is also a force parallel (as a component of weight) you must ALSO overcome, what is the TOTAL force you must apply to push the cart up the ramp at a constant speed? ____ _75.79_ _______ N