Download Net Force, Mass and Acceleration activity

Name______________________________
Net Force, Mass and Acceleration activity
We have already studied objects at rest and learned that they have a total – or ‘net’ – force of
zero; that any forces in a particular direction are canceled out by one or more forces in the
opposite direction.
Purpose:
This activity will help you investigate the effect of unbalanced forces, net force that does not
equal zero.
If objects at rest have zero net force, then what motion results when net force is not zero?
Complete the following two hypotheses:
A) If the net force on an object were doubled, then
__________________________________________________________________________,
because ___________________________________________________________________.
B) If the mass of an object were doubled, but the net force remained constant, then
__________________________________________________________________________,
because ___________________________________________________________________.
Set-Up
.
1. Log into a computer and start LoggerPro
2. Download the ‘Fnet activity’ file from the website; unzip the file
3. Connect the force sensor and accelerometer (mounted on a Dynamics Cart) to the
computer; be sure LoggerPro shows data from both sensors.
4. Launch the Fnet activity file
5. Set the cart on a horizontal track and make sure it is at rest and no one is touching it.
Then ‘zero’ the sensors (by clicking the blue “0” on the toolbar) and ensure that the
computer reads zero acceleration, and zero force when the cart is at rest and no one is
pulling on it.
6. Display three graphs on your screen (they may be separate graphs or all three on one
large graph): Force vs. Time, Acceleration vs. Time, and Velocity vs. Time
7. push the cart back and forth on the track by holding only the metal hook on the force
sensor. Push the cart with varying degrees of force (small, medium and large) to get a
range of values for force acceleration, and velocity. Since the cart is designed to have
low friction, the force recorded by the sensor is very close to the net force on the cart.
Analysis
1) Looking at your three graphs, which two are most closely related?
2) Sketch the shapes of three graphs (net Force, Acceleration, and Velocity vs. Time) to
support your answer above.
3) How can we see from your data that net force causes acceleration?
Now, looking at numerical data
4) Choose 3 points with different force values (crests or troughs only) and determine the
acceleration at these times by using the data table or the numbers in the lower left of
the graph. For comparison, pick 2 of the values so that force is doubled in one of the
points (i.e. 2 N and 4 N).
time (s) ______
force (N)______
accel.(m/s/s)_______
mass(Kg)_______
time (s) ______
force (N)______
accel.(m/s/s)_______
mass(Kg)_______
time (s) ______
force (N)______
accel.(m/s/s)_______
mass(Kg)_______
What patterns do you notice?
What can you conclude about your ‘hypothesis A’ based on your data? (if you cannot make a
conclusion yet, feel free to take more data – but record it)
Now focus on ‘hypothesis B’
Change the mass (try and get the new mass to be about double the original mass) of the cart
and record the new mass (Kg) _________. Tape the mass securely onto the cart.
5) How does additional mass affect the graphs?
6) Choose 3 points with different force values (crests or troughs only) and determine the
acceleration at these times by using the data table or the numbers in the lower left of
the graph. Try to pick a point with the same force as in your earlier data.
time (s) ______
force (N)______
accel.(m/s/s)_______
mass(Kg)_______
time (s) ______
force (N)______
accel.(m/s/s)_______
mass(Kg)_______
time (s) ______
force (N)______
accel.(m/s/s)_______
mass(Kg)_______
How does the change in mass affect the ratio of Force to acceleration?
7) What can you conclude about your ‘hypothesis B’ based on your data? (if you cannot
make a conclusion yet, feel free to take more data – but record it)