Momentum and Force Lab

Materials: School Network and Macintosh Computer w/Interactive Physics

Time Allotment: 3 Class Days

Purpose:

AAA

Getting Ready:

This lab must be done on a Macintosh computer connected to the school network or upon a computer in the Science Computer Lab. To prepare for the lab, do the following steps.

  1. Open the Physics Explorer application (Two Bodies model) by double-clicking on its icon; it is found in the directory /Local Drive/Physics/Physics Explorer/Two Bodies.
  2. Choose Open... from the File menu and navigate to the Physics 163/Unit 4 folder of the same directory.
  3. Open the file titled Exploring Two Bodies by double-clicking on its name. A Physics Explorer simulation is opened.
  4. Open the file titled Momentum and Force using the appropriate button in the bottom window. Check that the middle window appears as shown below.

 

Make a Prediction:

If you've ever driven a car, you know that the faster you're going, the more room you need to slow down. As a rule of thumb, safety experts recommend that you leave a minimum of one car length between you and the car ahead of you for every 10 miles per hour that you are traveling. If your car is heavily loaded, it may take even a longer distance to stop. A question arises: How does a car's speed and mass affect its stopping distance? Tricky question: Which stops more quickly - a lighter car traveling at high speed, or a more massive car traveling more slowly?

In this lab you will study the braking behavior of model vehicles with different mass and velocity, and find out what affects the braking time and the braking distance.

1.Practice Runs

a. Click on the "Momentum and Force" button in the Selecting Exploring Activity window.

Imagine you are looking at the remote controls for two model vehicles, a car (the patterned object) and a truck (the solid object). The "Go" button sets the vehicles in motion. The "Brake" button has the effect of gradually bringing them to a halt, like taking your foot off the accelerator and stepping on the brake pedal. The braking force is assumed to be the same for the two vehicles, independent of vehicle weight.

The Velocity Graph lets you watch how the velocities of the vehicles change during the course of the simulation. You also have controls for changing the mass of the vehicles and their initial speed.

To adjust the brakes click on the "Adjust Brakes" button. In the Braking force window, change the breaking force to 250 Newtons by clicking on the "Plus" or "Minus" buttons repeatedly. (The buttons change the force in increments of 25 Newtons.)

b. With the HAND tool, click on the "GO" button in the Control window (the middle window). Both vehicles have a velocity of 40 m/s in the x-direction and a mass of 50 kg.

 

2. Braking Time

a. Increase the velocity of the car to 80 meters per second, and reduce the mass to 25 kg.

 

 

b. Now run the simulation. Record the actual results here:

Diagram:

 

Graph:

 

 

c. Using data from both car and truck, run the simulation three times to complete the first three lines of the following table:

Mass

(kg)

Velocity

(m/s)

Momentum

(m*v)

(kg*m/s)

Braking Force

(N)

Stopping

Time

(sec)

40

2000

250

80

2000

300

2000

400

 

 

 

3. Braking Distance

a. Now that you know how the two vehicles behave in terms of braking time, we will look at what affects their braking distance.

Mass

(kg)

Velocity

(m/sec)

Braking

Distance (m)

50

20

50

40

50

60

50

80

50

b. Look carefully at the values of speed and braking distance in your table. Can you see a relationship between them? What happens if the speed doubles? If it quadruples (speed increased by four times)?

c. Can you write a general expression that relates braking distance to velocity? (Hint: one of the terms is squared.)

d. Which do you think will have a greater affect on braking distance; doubling the mass or doubling the speed?

Mass

(kg)

Velocity

(m/s)

Braking

Distance (m)

50

40

50

80

100

40

 

 

 

Conclusion:

Describe the variables which effect the stopping time and the stopping distance of a skidding automobile. In your description, use phrases such as "inverse", "directly", "first power", second power". etc. Be complete and clear in your description. Do a bang-up job.

 

 

 

 

 

 

 

 


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This lab created by Tom Henderson and last updated on 11/26/97.

Special thanks to lab assitant Dan Reid for assistance with the typing.