5.2 Circular motion

Question 1

What are radians a unit of?

Answer 1

Angle.

Question 2

How do you convert degrees to radians?

Answer 2

To convert an angle from degrees to radians,
divide it by 360 and then multiply by 2π.

Question 3

What is meant by the period of an object
in circular motion?

Answer 3

The time taken for one full rotation.

Question 4

What is meant by angular velocity?

Answer 4

The angle travelled through divided by the
time taken.
This is similar to linear speed, except we’re
interested in rate of rotation rather than
distance/time.

Question 5

What kind of force is required to keep an
object moving in a circle at constant
speed?

Answer 5

A constant centripetal force (a force
applied always towards the centre of that
circle).

Question 6

True or false: The centripetal force and
velocity of an object moving in a circle
are always in the same direction.

Answer 6

False.
Velocity is always at a tangent to the circle,
force is always along a radius. They are
perpendicular.

Question 7

True or false: The centripetal force and
velocity of an object moving in a circle
are always in the same direction.

Answer 7

False.
Velocity is always at a tangent to the circle,
force is always along a radius. They are
perpendicular.

Question 8

How are linear and angular velocity
related?

Answer 8

v = ⍵r

Question 9

An object moving in a circle at a constant
speed is not accelerating. True or False?

Answer 9

False.
The direction is always changing hence
the velocity always changing which
means it is accelerating.

Question 10

What equation gives acceleration in
terms of angular velocity?

Answer 10

a=⍵²r

Question 11

What is acceleration in terms of linear
velocity?

Answer 11

a = v²/r

Question 12

What are the equations for centripetal
force?

Answer 12

F = mv²/r
or
F = m⍵²r

Question 13

Describe the steps how one can
investigate circular motion via an
experiment

Answer 13

● Circular motion can be investigated experimentally by tying a bung, with mass m, to a
piece of string, and threading it through a glass tube.
● The other end of the string has a weight, with mass M, suspended from it. This provides
the centripetal force, F =Mg, as the tension throughout the string is constant.
● The string is whirled in a circle, and the time taken for a complete rotation is recorded.
● The mass of the weight is altered and the experiment repeated.
● We equate Mg and the centripetal force mv²/r so Mg=mv²/r
● By measuring the radius of the circle and using the time for one complete oscillation,
the velocity can be determined. When v^2 is plotted against M, a straight line graph
which passes through the origin should be produced.