F&M Activity II–D3

How are Motion and Force Related?

Name:

 

Group:

 

Class Period:

 

 

Introduction: In this on-line sample activity, clicking on the links to the “simulators” will open snapshots of simulator setups in a separate window. These snapshots are organized into “slide shows” of two different simulation runs. Clicking on Run advances a slide show to the next frame, while Rewind returns to the last frame you viewed. Clicking on Stop takes you to a slide show’s final frame.

 

 

 

When playing soccer, as a player moves along the field with the ball, he or she keeps it moving with a series of little kicks, or pushes. How do these little pushes make the ball move?

 

 

 

Materials: cart, level track

 

 

 

In the first activity you explored the conditions necessary to keep an object at rest. In this activity you will begin to explore how a force influences the motion of an object. You will be working with a cart moving along the smooth track, and for simplicity you can ignore any affects due to friction.

 

 

 

1.      Set up the cart and track. The first thing to do is related to what you did in the last activity. Give the cart a brief, moderately strong push with your finger, so that after it leaves your finger it will travel along the track without noticeably speeding up or slowing down. (If it does not do that, try leveling the track.)

 

 

 

 

 

 

2.      For the situation described above, predict the speed-time, acceleration-time, and force-time graphs by sketching approximate graphs below. Let t = 0 correspond to when you started to give the cart its brief push.

 

 

 

One Push

 

 

 

 

How did you decide?

 

 

 

 

 

 

 

 

3.      Now give the cart a quick push to get it started, then a second push when it is part way along the track, and then a third quick push when it is further along the track. Observe what happens, then predict speed-time, acceleration-time, and force-time graphs for this motion by sketching approximate graphs below.

 

 

 

 

 

One Push, then a Second Push, then a Third Push

 

 

 

 

How did you decide?

 

 

 

 

 

 

 

 

4.      To get feedback on your predicted graphs, you will use the Simulator. When you open it you will see a round object (representing the cart), and a black triangular-shaped object attached to it called a “thruster.” The thruster can deliver a “push” to the object. It is activated (that is, it gives a “push”) whenever you press on the keyboard space bar, and the push lasts as long as you hold down the space bar. The simulator also displays speed-time, acceleration-time, and force-time graphs. Open the simulator, turn it on and immediately press the spacebar for about one second, then release it. The motion should continue for 10 seconds and will stop all by itself. Take a snapshot of the three graphs and paste it below. This will correspond to the case of giving the cart ONE PUSH. Click here to open the simulator: Act II-D3 Sim.

 

 

 

One Thrust

 

 

 

 

5.      Return to the Simulator and rewind the movie. To clear each graph, click on the “c” or the “dot” at the upper right of each graph once or twice. This time, turn the simulator on, then press the space bar for about one second, and release it. Then after another two seconds, press the space bar again for one second. Then after two more seconds, press it again for one second. This motion would correspond to the second motion above. Take a snapshot of the graphs and paste it below.

 

 

 

One Thrust, then a Second Thrust, then a Third Thrust

 

 

 

 

6.      Compare the graphs constructed by the simulator with those you had predicted. Are there any differences, and if so, what are they?

 

 

 

 

7.      Use the graphs to answer these questions:

 

 

 
  1. During those times when the speed of the object is constant, is the strength of the unbalanced force acting on the object equal to zero or greater than zero?

 

 

 

 
  1. During those times when the speed of the object is changing (that is, the object has an acceleration), is the strength of the unbalanced force equal to zero or greater than zero?

 

 

 

 
  1. Do your answers to parts (a) and (b) make sense?

 

 

 

 

8.      Which two quantities seem to be more closely related; that is, which two seem to "go together": force and speed, or force and acceleration?

 

 

 

 

How did you decide?

 

 

 

 

 

 

9.      Open your Cycle II Idea Journal. Based on evidence gathered in this experiment, change or add ideas for the following: Friction Idea; Motion with an Unbalanced Force Idea; Motion without an Unbalanced Force Idea.