Name
Period
Date
Central Force Lab
Purpose:
To create graphical and mathematical representations of the relationship between
the force, the radius, the mass, and the speed of an object moving in a circle at a
constant speed.
Procedure:

Navigate to the Uniform Circular Motion simulation page on the Physics
Classroom website.
Experiment with the on-screen buttons in order to gain familiarity with the control
of the animation. The object speed, radius of the circle, and object mass can be
varied using the sliders or the buttons. A trace of the object's motion is shown.
The magnitude of the net force is displayed in the animation window. The
animation can be started, paused, continued or rewound.
In each case, graph the variables and linearize if necessary. Sketch the graph(s)
and record the linear regression information. Since this is a simulation, we don’t
need to average the class results.


Force vs. Mass
Force vs. Speed
Force vs. Radius
Mass
(kg)
Force
(N)
Speed
m
s
 
Force
(N)
Radius
(m)
0
0
0
0
10.
2.0
10.
20.
5.0
15
30.
10.
20.
40.
15
25
50.
20.
30.
60.
Radius = 30. m
Speed = 20. m
s
Radius = 30. m
Mass = 10. kg
Force
(N)
Speed = 20. m
s
Mass = 10. kg
Central Force Lab
page 2
1. Thinking Mathematically:
Use the relationships found above to answer the following questions. Circle the
correct answers.
a. For constant radius and speed, state the relationship between the force acting
upon the object and its mass.
b. If only the mass of the object is doubled, the force is (one-half, one-fourth, two
times, four times) the original value.
c. For constant radius and mass, state the relationship between the force acting
upon the object and its speed.
d. If only the speed of an object is doubled, the force is (one-fourth, one-half, two
times, four times) the original value.
e. If only the speed of an object is tripled, the force is (one-third, one-ninth, three
times, nine times) the original value.
f. For constant speed and mass, state the relationship between the force acting
upon an object and the radius of the circle in which it moves.
g. If only the radius of the circle is doubled, the force is (one-fourth, one-half, two
times, four times) the original value.
h. If only the radius of the circle is cut by one-third, the force is (one-third, oneninth, three times, nine times) the original value.
RESET the simulation, turn on the Velocity Vector and press START.
2. In the diagram at the right, a variety of positions
about a circle are shown. If the object is moving
clockwise, draw the velocity vector at the various
positions; direct the velocity arrows in the proper

direction and label them as v .
3. TRUE or FALSE? If an object moves in a circle at a constant speed, its velocity
vector will be constant (meaning exactly the same!). Explain
your answer.