Laboratory Activity 5: Force and Motion

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Objectives

  • Explore how force is related to acceleration and velocity.
  • Develop a quantitative understanding of the force relationship.
  • Learn about proportional and inversely proportional graphs.

Equipment

  • Computer
  • Ultrasonic motion sensor
  • Force sensor
  • 2 USB Links
  • Dynamics cart
  • Track for cart
  • Cart masses
  • Pulley to mount on end of track
  • String or fishing line
  • Wire hook for weights
  • Masses for hanging.

Activity One: Force and motion

Prediction 1: Using the line tool on the drawing toolbar of Word, draw a line on both the velocity, acceleration and force graphs below predicting the shape of a curve for a cart starting at rest and being pulled with a constant force.

Set up the equipment: Obtain 2 USB Links, a force sensor and a motion detector. Plug the USB links into the USB hub (small plastic black box) and plug that into the computer and the power source. Open the experiment file called MotionAndForce.ds to display force, acceleration and velocity graphs. You can find it by going to the networked disk “PLAB” (usually disk G:), in that opening the folder “Plab”, then finding the folder for Physics 201, and then looking in the folder for Lab 4. Set the track on the table so one end is hanging off, place the motion detector at the other end. Attach the pulley so that it is on the end off the table. Attach the force sensor the cart on the magnet side by using the screw. Make sure the screw goes through the hole labeled “cart” and not “IDL bracket.” Hook the length of fishing line on the hook of the force sensor, run it over the pulley, and hang the wire mass hook on the end. Place both of the black cart masses on the cart.

Experiment: Place the cart on the track about 30 cm (1 foot) away from the motion detector and turn it on, with one person holding it in position. Have another team member start taking data. Let go of the cart as soon as the clicking sound is heard, careful to not get any hands between the detector and the cart, and let the cart speed away. Catch it just before it crashes into the other end of the track. When you have a nice graph, copy the graph and paste it in the section below.

-pas
te graph here-

Question 1: How did the result compare to your prediction? Explain how the velocity, acceleration graphs are related.

The velocity matched the prediction, but the other two did not. The velocity and acceleration graphs are increasing by small amounts.

Experiment 2: Measure the average force and average acceleration of the cart during the time it is moving freely. Do this by click-dragging a rectangle around the data points with the mouse, and then selecting “mean” from the “Statistics” button at the top of the window. Record the force and acceleration in the chart below. Add masses to the wire hanger hanging at the other end of the string and repeat.

Force (N) / Acceleration (m/s2)
Hanger alone / 0.238 / 0.059
Hanger + 10 g / 0.432 / 0.202
Hanger +20 g / 0.526 / 0.223
Hanger +30 g / 0.609 / 0.384
Hanger + 40 g / 0.753 / 0.556

Then enter the force and acceleration data in the table in DataStudio. A graph of Acceleration vs. force will be automatically created for you. Paste that in the space below.


Question 2: How does the acceleration relate to force? Can you write down a mathematical expression?

Acceleration is proportional to the net applied force. a= EF/ m

Experiment 3: Repeat the previous experiment, except this time keep the mass on the hanger the same and vary the mass of the cart. Using the scale in the classroom, find out how much your cart weighs with the force sensor, and then each cart mass. Place 10 or 20 grams on the hanger, and then take all the masses off the cart. Do the experiment, recording the total mass of the cart and the acceleration. Repeat for the cart + 1 mass, then with 2 masses, and so forth. Share masses at your table if you need to.

Mass (kg) / Acceleration (m/s2)
Cart and force sensor / 0.349 / 0.266
Cart, sensor & 1 mass / 0.597 / 0.205
Cart, sensor & 2 mass / 0.845 / 0.204
Cart, sensor & 3 mass / 1.093 / 0.159
Cart, sensor & 4 mass / 1.341 / 0.086

Then enter the force and acceleration data in the hidden table in DataStudio. Look in the navigation window in the lower left corner, and click on the second data table. A graph of Acceleration vs. Mass will be automatically created for you in the third graph, which you will have to click on in the same navigation window. Paste that in the space below.


Question 3: How does the mass relate to force? Can you write down a mathematical expression?

The greater the mass, the less the acceleration for that same net force.
EF=ma

Summary

The following questions will help you get the main ideas out of this lab. You should find these straightforward questions, but take the time to talk it over with your team and write complete answers to these questions. You may find your answers here to be the most useful part of this lab down the road.

Summary 1: Force is directly related to which of the motion quantities? How does changing the force change its motion?

Force is directly related to acceleration. Changing the force changes how the speed of the motion

Summary 2: How does mass affect motion and force? Can you write down an expression that relates force, mass and acceleration?

The mass of an object can speed an object up or even slow it down.
EF=ma

Summary 3: How do you know your above statements are true? What experimental observations and/or logical reasoning can you give to justify what you said in summary questions 1&2?

From the observations of the following experiment.