Forces and Friction: PhET Lab Introduction: Friction is defined as the resistance that one surface of object encounters when moving over another. It is Friction between two surfaces arises from interaction between molecules on the surfaces. We have two kinds of friction: kinetic friction and static friction. motionbod cen bodies. Both friction forces act along the surface, in the opposite direction of motion or expected Consider the box shown above in figures a through d. When it is at rest and no horizontal force is applied, force, static friction is going to Oppose that force to keep the object at rest. In () magnitude of tension is equal to the static friction because the object is still at rest. We can keep increasing tension and the static friction will also increase. The system will stay in equilibrium and at rest. But when we get to a point friction can not oppose to the force anymore. As soon as the motion starts (d). the friction turns to kinetic The static friction force can vary between zero and its maximum value: osf.sun. fumax) = Man In other words, maximum static friction is equal to static coefficient friction times the normal force. When the system is using maximum static friction, it means object is just about to move. As soon as motion recedure: Click on "simulations" - "Physics" - "Motion" - "Forces a basics" - Download or run Static and Kinetic Friction 1. In the menu, select the friction simulation. forces and Motion: Basics 2. Play with the a keep all of them checked for applying different forces. or your experiments. Play with moving objects and 3. Keep the friction button in the middle and don't change it throughout this experiment. ormal force) and explain what happens orce on the 50 kg object. Draw the free body diagram (don't forget to . Now. slowly increase the applied force (in one New the button shown below). until you start the motion. What is the maximum applied force that did not start any motion? 0 Newtons Maximum applied force before motion starts: mum force will be equ um static friction force. Based on this nformation, calculate the static coefficient of friction. Show your calculations below. Calculations: Static Coefficient of Friction: 7. Apply 150N on our 50kg object. the free body diagr b) What is the value of kinetic friction force? ) Calculate kinetic coefficient of friction. Show your calculations below. Calculations: Kinetic Coefficient of Friction: 1) Calculate the acceleration of the object. Show your calculations below. Calculations: Acceleration:_ Repeat the experiment for the objects using simulations, determine or calculate unknowns Mass (kg Friction (N) H. Kinetic friction (N) 90 kg box and girl 100 kg (two boxes or thrash can ( box and man ) . Now. let's use the object with the unknown m s (gift box). By using the procedure we developed, determine Maximum static friction: Using the maximum static friction formula, find the unknown mass. Show your work: Kinetic friction: Using the kinetic friction formula, find the unknown mass. Show your work. Does it match with your above answer? the table below, determine the kinetic friction and s he kinetic friction and sum of forces from the simulation and calculate us and acceleration to fill out the table. Mass (kg) Kinetic friction (N) forces (N) Acceleration (N/kg) (box and girl) 350 N 100 kg two boxes or thrash 350 N can 130 kg box and man 350 N Questions 1. Which is higher: static friction or kinetic friction? 2. Which is higher: static friction coeff . As the mass of an object increases moving the object? Explain. unt of force needed to begin Does the kinetic friction depend on applied force? Does it change if you increase the applied force while object is moving? Explain. . Does the force of kinetic friction depend on weight of the object? Explain. 5. Does the coefficient of kinetic friction depend on the weight of the object