Dynamic Force Modeling Activity for Modeling with Simulation workshop

Modeling Activity using this #html5 simulation

No Net Force (no Push Force )Model

Tom has just been promoted and is pushing a file cabinet down the hall to his new office. He begins by looking at the file cabinet and considers how to best go about his task. Select Fx = 0 to model the zero force model. Note the motion of the block is no change in position and velocity is zero all the time.

Activity 1: Using the model builder, select Fnet_x = 0 to simulate this effect

No Net Force ( 0<|Push| => Maximum Static Friction) Model

He then begins pushing on the file cabinet, which, at first, does not move at all. To simulate this case, select Push to be 3 N and observe what happens to the motion of the block. Note that the Push is cancel out by the Friction Force. Even at Push = 4.905 N is balanced out by Friction Force and the block does not move.

Activity 2: Using the model builder, select Fnet_x = 0 to simulate this effect

Just Enough Push force (Push> Maximum Static Friction) to move Model

He pushes it slightly harder than the maximum static friction, and it is sliding . Thus, applying a Push force just larger than 4.905 N, the object begins to slide. But at t >0, the Friction becomes Kinetic Friction. 

Eventually the file cabinet begins to slide across the floor, slowly moving towards his new office with acceleration.   

Activity 3: Using the model builder, select Fnet_x = 3.038 to simulate this effect. note that the static force is just a force to overcome initial when v = 0, after |v|>0, kinetic friction replaces as the frictional force.

Big Idea

Thus, the evidences and model building process above suggests the condition of acceleration is the presence of non zero net force, which is F = ma, Newton's Second Law.

Misconceptions

Students may think that it is possible to experience is pushing the file cabinet, and it is moving to the right with constant velocity.