Lab 3 Acceleration Due to Gravity!
Objective
The purpose of the lab is to measure the acceleration due to gravity during free fall and to observe
cases when free fall does not apply.
Equipment
Motion sensor, rubber ball, wooden board.
The Acceleration Due to Gravity
The acceleration due to gravity at the surface of the Earth is constant. It has a magnitude of 9.807
m/s2. It is in the downward direction. According to Newton’s second law of motion, when an
object is affected by Earth’s gravity only, it will accelerate at the rate. This is called free fall. An
object that does not have this acceleration must have other forces acting on it.
Experiment 1: Bouncing Ball
Place the motion sensor’s face about 1 m from the table or the floor facing down.
picture on the right. Set it to record at 50 Hz.
See the
Drop the ball from a height about 10 cm below the motion sensor. Attempt to acquire the following
position as a function of time data. In order to do this, minimize the rotation of the ball or put the
right amount of spin on it to keep it directly under the sensor.
Record three bounces of the ball which will contain two airborne sections as well. See the sample
diagram.
position
time
page 1
When interpreting the data, remember that the motion sensor measures the distance of the object
in front of it. Also, the direction pointing away from the motion sensor is the positive direction.
We will look at the data in the regions shown below.
bounce 1
bounce 2
bounce 3
position
time
leg 1
leg 2
leg 3
leg 4
To find the acceleration, display the velocity vs time graph. Identify the regions in the velocity
graph that correspond to the regions above. For each region, determine the slope of the velocity
graph. This is the acceleration. Include the uncertainty of the dlope.
Make a table of the regions above.
regions
acceleration
(m/s2)
net force
direction
probability of
agreement
free fall? (Y/N)
bounce 1
leg 1
leg 2
bounce 2
leg 3
leg 4
bounce 3
For the acceleration, indicate the magnitude and the (real-life, up or down) direction. Indicate the
direction of the net force on the ball.
Indicate, also, the probability of agreement between the experimental acceleration and the
expected acceleration for free fall. Calculate this as the probability that the result will fall within
5% of 9.8 m/s2. Since the data was taken by a machine, the 5% tolerance is larger than
necessary, but it’ll show us just how good it is.
Question 1
In which regions do the data indicate that the acceleration is likely completely due to gravity so
that we can conclude that it is in free fall?
page 2
Experiment 2: Falling Board
Repeat the above experiment with a falling wooden board. Drop it on a piece of foam. Of course
it will not bounce so there is only one leg.
regions
acceleration
(m/s2)
net force
direction
probability of
agreement
free fall? (Y/N)
leg 1
Question 2
Does the data indicate that the acceleration is likely completely due to gravity so that we can
conclude that it is in free fall?
page 3