Centripetal Force Experiment
Physics
Name:
Period:
In this experiment we will look at the centripetal force exerted on a ball as it whirls above your head.
We will calculate the centripetal force necessary to make it turn based on the speed and mass of the ball
and the radius of its circle. We will then compare that number to the actual centripetal force provided by
the apparatus.
We will see how the necessary centripetal force depends on the radius and velocity of the circling
object in two different experiments.
Apparatus
Our apparatus consists of a golf ball on the end of a piece of string. You will twirl the golf ball around
above your head. The tension in the string will provide the
centripetal force to keep the golf ball from flying off in a straight
line (to keep it turning).
The string runs through a glass tube, which we will use as a
handle. The glass is smooth enough that it has very little friction
with the string, so it allows the string to slide up and down to
adjust to the situation.
The string has a loop on the end beneath the handle to hang a
weight so that we can control the amount of tension in the string.
The actual tension that the string exerts on the golf ball will be
equal to the force of gravity on the weight hanging on the string.
Procedure
0. Measure the mass of the golf ball:
. You will need it for calculating centripetal force.
Part 1: Speed vs. Tension
1. Measure out 50 cm from the center of the golf ball and slide the glass tube so that its top is 50 cm
from the center of the golf ball. Place your paper clip around the string just on the other side of the glass
handle. This will serve as a marker – while you’re spinning the ball around, you want to keep the paper
clip just beneath the end of the glass tube so that the ball remains spinning in a 0.50 m radius circle.
2. Hang a 100-g mass on the lower end of the string. Record the hanging mass in the Actual Tension
section of the data table.
3. Twirl the golf ball around over your head so that it stays even with the paper clip right below (not
quite touching) the glass tube.
4. To find the velocity of the ball, you will use your stopwatch to time how long the ball takes to make
10 complete circles around the spinner. Enter your results in the data table
5. Repeat steps 2 – 4 with a 200-g mass, a 300-g mass, a 400-g mass and a 500-g mass.
6. Calculate the actual tension that the string exerts on the whirling golf ball by finding the force of
gravity pulling on the hanging mass. Show your work underneath your data table.
7. Find the distance the ball travels when it makes 10 complete circles (Circumference = 2r) and then
use the distance and time to find the speed. Show your work underneath your data table.
8. Calculate the centripetal acceleration and centripetal force needed to keep the ball moving in the
circle that it follows. Show your work underneath your data table.
Part II: Speed vs. Radius for Constant Tension
1. Hang a 200 g mass on the end of your string.
2. Adjust your string so that there are 100 cm of string above the glass handle. Reposition your paper
clip.
3. Whirl golf ball on the string over your head and time 10 complete circles. Record your time in the
space provided.
4. Repeats steps 2 and 3 with the string set to be 0.8 m, 0.6 m, 0.4m and 0.2 m long respectively.
5. Find the distance for the 10 complete circles (Circumference = 2r) and then use the distance and
time to find the speed. Show your work underneath your data table.
6. Calculate the centripetal acceleration and centripetal force needed to keep the ball moving in the
circle that it follows. Show your work underneath your data table.
Questions:
Part I: Speed vs. Tension
1. Look at the results for your two calculations for the force acting on the golf ball – the force of gravity
on the hanging mass (which makes the string pull on the golf ball) and the amount centripetal force
needed to make it turn. How do your two columns of numbers compare? Give the overall comparison
as well as any specific cases that stand out.
2. a) What is the relationship between the golf ball’s speed and the amount of force applied to make it
turn in a circle that is 0.5 m in radius? How did you have to adjust the speed when you increase the
force you were applying?
b) Explain in terms of basic concepts and measurements why this relationship exists. Why does the
amount of force you apply change when you change the ball’s speed and vice-versa?
3. a) What is the relationship between the ball’s velocity and the radius of it’s circle when you don’t
change the force you apply? How did you adjust the ball’s speed when you allowed the ball to spin in a
larger circle?
b) Explain in terms of basic concepts and measurements why this relationship exists. Why does the
ball’s speed change when you adjust the radius of the circle?
Data Table – Part 1: Speed vs. Tension
Actual Tension
Hanging Mass
Fg
Golf Ball
Mass
Time
(10 circles)
Finding Speed
Radius
Distance
Speed
Data Table – Part II: Speed vs. Radius with a Constant Tension
Hanging Mass:
String
Length
Actual Tension: Fg =
Time
(10 Circles)
Distance
Speed
aC
FC
(Tension)
aC
FC
(______)