Rotational Motion Flashcards
What is meant by Torque (sometimes called the moment of a force)?
Torque is the turning effect of a force on a rotating object.
What relationships would you use to convert between:
- Linear displacement and angular displacement
- Linear velocity and angular velocity
- Linear acceleration and angular acceleration
For any of these relationships, you would multiply the angular quantity by the radius of circular motion to get the linear quantity:
What does the prefix f stand for?
f = femto = x 10-15
How would you find the instantaneous velocity of an object from a displacement-time graph such as this?
Take the gradient of the line.
If the graph is a curve, take the gradient of the tangent to the curve at a point.
Which two things does the moment of inertia of an object depend on?
- The mass of the object
- The distribution of mass around a given axis of rotation (which can be quantified with the radius, r)
What does the prefix M stand for?
M = mega = x 106
What is the unit of angular displacement?
Radians (rad)
[note: rads is incorrect]
What does the prefix G stand for?
G = giga = x 109
What does the prefix m stand for?
m = milli = x 10-3
How is angular acceleration defined in terms of angular velocity?
Angular acceleration is defined as the rate of change of angular velocity.
What is the unit of moment of inertia?
kg m2
What does the prefix p stand for?
p = pico = x 10-12
How is angular velocity defined in terms of angular displacement?
Angular velocity is defined as the rate of change of angular displacement:
What is the unit of Torque?
newton-metres (Nm)
What is the unit of angular acceleration?
rad s-2
What does the prefix k stand for?
k = kilo = x 103
What does the prefix P stand for?
P = peta = x 1015
What is the unit of centripetal acceleration?
ms-2
What is the unit of angular velocity?
rad s-1
Convert 360° into radians.
360° = 2π radians = 6.28 rad
The following experimental setup can be used to determine the moment of inertia of a disc which is allowed to rotate on a frictionless air bearing turntable.
Explain the measurements which will need to be taken, and how to use these to determine the moment of inertia of the disc.
Find the torque applied to the disc by using the relationship T = Fr.
Use the light gate to measure the angular acceleration of the disc.
Vary the hanging mass to vary the torque, and repeat a few times.
Plot T against α, and take the gradient of the straight line which will be equal to the moment of inertia of the disc.
What is the definition of moment of inertia of an object?
The moment of inertia of an object is a measure of its resistance to angular acceleration about a given axis.
How would you find the instantaneous acceleration of an object from a velocity-time graph such as this?
Take the gradient of the line.
If the graph is a curve, take the gradient of the tangent to the curve at a point.
Which two quantities does the rotational kinetic energy of an object depend on?
Moment of Inertia and angular velocity