Newton’s Second Law – Part 2
Purpose:
Determine if any plausible relationship exists between force, acceleration and mass.
Present any relationship in terms of a formula.
There are three variables that we want to study. We can only vary (change) one of them at a time and still be able to draw meaningful conclusions. We will therefore do this experiment in two parts:
1.
We will examine the relationship between mass and acceleration.
2.
We will examine the relationship between force and acceleration.
Procedure: We will use a motion sensor to graph the motion of a cart that has a constant mass with a changing amount acting on it. (That force is gravity acting on the hanging weight).
IMPORTANT: The force is acting to change the motion of the hanging weight AND the cart. We will refer to the total mass of everything that is moving as the System Mass. (We will ignore the mass of the string, since it is so small)
Motion sensor
Cart Book
Hanging weight
1) Make a hypothesis for the relationship between acceleration and force.
I’ll make it easy for you. Complete this sentence:
“As more force is added to the system, the acceleration will…
2) Collect data

Open the file on your desktop called “Second Law with Motion Sensor”

Three graphs should appear: Position vs. time, velocity vs. time, and acceleration vs. time.

Pull the cart back towards the motion sensor until the hanging weight is just below the pulley. Hold onto the cart near its front so your hand doesn’t get in the way of the motion sensor.

Click on the “collect” icon or just push the space bar. Release the cart when you hear the sensor start to click.

Newton’s Second Law – Part 2
The motion sensor is only collecting information about the cart’s position as time goes by. The velocity and acceleration are calculated from the position data. Errors or inconsistencies are amplified, making it hard to get a good graph of acceleration. The upshot of this is that you will have to do several trials. If you don’t get a good graph, then you should just throw out that trial and try again.
It should look something like this. The bottom graph is acceleration. It should be essentially straight during the time that the cart is moving. (You can tell when the cart is moving by looking at the position graph).
You will want to highlight a section of the acceleration graph where the cart is moving and the line is mostly straight.
Click on the “statistics” icon

Newton’s Second Law – Part 2
Example: Trial “a” is probably straight enough to use, but trial “b” is too wavy. If you are in doubt, try again; we have plenty of time. (Be aware however, that you will rarely get a perfectly straight graph)
3) Graph your data using Excel.

Enter values for the x-axis in the first column

Enter values for the y-axis in the second column

Highlight all of your data and select “insert chart”

Choose a scatter plot

Be sure to include a title and axis labels

See Mr. Mower for help with a trendline before you print your graphs

1.0 N
1.5 N
2.0 N
2.5 N
Newton’s Second Law – Part 2
For Part 2 you will keep the amount of system mass constant, while changing the pulling force acting on the system. Measure the average acceleration of five trials for each amount of pulling force. (The system includes the hanging mass, the cart, and any additional mass on the cart).
Important: You will increase the pulling force by adding more mass to the hanging part. In order to avoid changing the system mass when you do this, the additional mass must already be part of the system. The additional masses will start off on the cart; to increase the pulling force, move mass from the cart to the hanging part.
When you are done, you will make a graph of acceleration (y-axis) vs. pulling force (x-axis). See the previous page for instructions for making graphs using Microsoft Excel.
The mass of my cart is __________kg.
pulling force on glider
Added mass on cart
(kg)
Hanging mass
(kg) total mass of system
(includes cart)
Trial 1
Acceleration m/s 2
Trial 2
Acceleration m/s 2
Trial 3
Acceleration m/s 2
Trial 4
Acceleration m/s 2
Trial 5
Acceleration m/s 2
Average acceleration m/s 2
0.5 N 2.2 kg 0.05
2.15 kg
2.1 kg
2.05 kg
2.0 kg
0.10
0.15
0.2
0.25