Newton's Second Law: How does acceleration change with varying forces?

This activity is designed for students to use distance and time to calculate velocity. This activity is designed for students to create graphs representing their collected data. This activity is designed for students to quantitatively analyze their data. Students will see that the acceleration of the cart depends upon the force pulling on the cart.

This is meant for 9th grade physical science students who have already studied motion and graphing. It should be done while studying Newton's laws of motion. This is a lab that can be done in one-90 minute period and is intended to be done in groups of 3-4 students. Students should be able to use simple algebraic equations to calculate velocity (v = d/t) and should be familiar with Excel or another computer graphing program.

Equipment:
-Lab carts
-Pulleys
-String
-Hanging or slotted masses
-Paper clips
-Washers

The students are given a worksheet [see file Force and Acceleration Lab] that has instructions for setting up the experiment. A lab cart is loaded with masses and is attached by a string to a paper clip that will hold washers to offset friction and the mass that will cause the cart to accelerate. The string is put over a pulley that is clamped to the lab table. The distance that the mass falls is recorded and is used to calculate the velocity of the cart. A stopwatch is used to determine the time it takes for the mass to fall that distance. Those are then used to calculate the velocity of the cart. Three trials are performed for each mass and then an average is calculated. The mass hanging on the string is increased and the experiment is repeated. Once trials have been completed for five different masses, the results are put into Microsoft Excel so the slope of the line (acceleration) can be calculated. A second graph of acceleration versus force is created to see if Newton's second law is supported by the experiment.

The lesson is introduced after Newton's first and second laws of motion have been discussed. Students are put into groups of 3-4 to complete the experiment and graphical analysis. After the lab is completed a group discussion is held covering the relationship between force, mass and acceleration. Assignment Handout (Microsoft Word 45kB Aug25 08)

When the students are divided up in groups, we discuss how each person should have a specific "job" in the lab such as timer, catcher, releaser, recorder, etc. and how they need to communicate and work cooperatively. We also discuss how changing who does what job can affect the results of the experiment.

Prior to doing this activity, we spend time reviewing the different parts of graphs; slope as well as the independent and dependent variables. I also show them in the prelab how to set up a graph in Microsoft Excel. If you do not have access to computers you could also have them create the graphs by hand and manually calculate the slope of the graph for acceleration, however I would advise you to plan for additional class time to complete the assignment.

The worksheet along with the created graphs are turned in to be assessed. I check the calculations on the worksheet, the format of the graphs (units, correct lines, title) and the discussion questions.

II.D.1 The student will use Newton's three laws of motion to qualitatively and quantitatively describe the interactions of the objects.

I.B.3 The student will apply mathematics and models to analyze data and support conclusions