Name: ______Block: ______Date: ______

Newton’s Second Law: The acceleration of an object is directly proportional to the net force applied, and inversely proportional to the mass.

Purpose: In this lab, we will observe, more or less quantitatively, the relationship between mass and acceleration. Using the iBook computers and motion detectors we will be attempting to validate Newton’s second law.

Pre-Lab:

1)  Draw the FBD of the cart as it rolls to the side (ignore friction). Include net force.

2)  Describe how would you move in front of a motion detector to produce a velocity graph like this:

·  Determine the change in velocity: Dv = ______

·  Determine the change in time: Dt = ______

·  Calculate the acceleration:

Set up:

This is a station lab. You don’t need to complete the stations in order, but make sure you record the data in the appropriate section/table. On each station you will find the set up seen in the previous page. On the computer screen you will see a velocity graph.

Ø  Constant: force

Ø  Variable: acceleration and mass

Goal

You will explore the relationship between mass of the cart and its acceleration: each station will have a different mass, and you will measure the acceleration of the cart.

Mass hanging from the string: mhanging = _____ kg

Weight of the mass hanging from the string:

Prediction

Write a prediction of what do you think will happen to the acceleration as you vary the mass on top of the cart:

Procedure

1.  Position the cart as close the detector as you can.

2.  Start the motion detector.

3.  Quickly, let the cart go.

4.  Look at the velocity graph and determine the change in velocity and change in time. Record those values in the table below.

5.  Repeat for all 6 stations.

6.  Go back to your table and finish calculating the average acceleration of the cart.

Data collection

Station 1

Mass of the cart: mcart = ______kg

Trail / Dv (m/s) / Dt (s) / Acceleration
equation / Plug in the numbers (with units) / acceleration (m/s2)
1 /
2 /
3 /
Average:


Station 2

Mass of the cart: mcart = ______kg

Trail / Dv (m/s) / Dt (s) / Acceleration
equation / Plug in the numbers (with units) / acceleration (m/s2)
1 /
2 /
3 /
Average:

Station 3

Mass of the cart: mcart = ______kg

Trail / Dv (m/s) / Dt (s) / Acceleration
equation / Plug in the numbers (with units) / acceleration (m/s2)
1 /
2 /
3 /
Average:

Station 4

Mass of the cart: mcart = ______kg

Trail / Dv (m/s) / Dt (s) / Acceleration
equation / Plug in the numbers (with units) / acceleration (m/s2)
1 /
2 /
3 /
Average:


Station 5

Mass of the cart: mcart = ______kg

Trail / Dv (m/s) / Dt (s) / Acceleration
equation / Plug in the numbers (with units) / acceleration (m/s2)
1 /
2 /
3 /
Average:

Station 6

Mass of the cart: mcart = ______kg

Trail / Dv (m/s) / Dt (s) / Acceleration
equation / Plug in the numbers (with units) / acceleration (m/s2)
1 /
2 /
3 /
Average:

Analysis

Using complete sentences answer the following questions:

1)  Describe the relationship between the mass and the acceleration of the cart. Use the following sentences: “As the mass of the cart increases the acceleration of the cart …” and “as the mass of the cart decreases, the acceleration of the cart …”

2)  In math, how is this relationship called? If you don’t know ask at least FOUR of your peers before you ask the teacher.

3)  Find the equation in your MCAS formula sheet that describes this relationship and write it down:

4)  Calculate the acceleration using this equation. Remember the force applied was the same for every station and compare it with the measured average acceleration. Tell whether the acceleration you measured was greater or less than you expected (calculated). Was it consistent? Describe what could have been causes for errors.

Station / mcart
(kg) / Force
(N) / Equation / Plug in the numbers (with units) / Calculated acceleration (m/s2) / Average acceleration (m/s2)
1
2
3
4
5
6

Extra credit

You will plot data and try to find a pattern. The acceleration is inversely proportional to the mass. To better see the pattern that mass and acceleration follow you will plot the acceleration of the cart versus the inverse or reciprocal of the mass.

ü  Find the inverse or reciprocal of the mass

x / y
m (kg) / 1/m (1/kg) / Average a (m/s2)

ü  Plot the acceleration vs. the reciprocal of the mass.

Use the space below to answer the following questions:

Does the data seem to be on a line?

What is the slope of the line?

What is the unit of the slope? Make sure you simplify using: 1 N = 1 kg m/s2

What quantity was measured in newtons in this activity? Hint: a quantity that was constant (the same) for all stations


Teacher’s notes:

ü  In the computer, open cart from physics with Venier.

ü  Change the grid line to solid grey, so they are visible for calculations

ü  Change velocity scale: 0-0.8 m/s

ü  Get rid of the position graph

ü  Get strings of the same length

ü  Fix the ends or the whole thing will fall to the ground with each drop (books seem to work fine)

ü  A small mass hanging down the string seems to work fine.