Module 5.2 - Circular Motion Flashcards
Define one radian
The angle subtended at the centre of a circle when the arc is equal in length to the radius of the circle
Define (time) period
Time taken in seconds for one complete circular path
Define angular velocity
Rate of angular rotation (measured in radians per second)
Define centripetal acceleration
Acceleration of an object moving with uniform circular motion
Directed radially inwards towards the centre of the circle, perpendicular to the velocity vector at any instant
How to convert from degrees to radians
Multiply angle by 2 pi and divide by 360
How to convert from radians to degrees
Multiply angle by 360 and divide by 2 pi
What is the difference between speed and velocity in relation to circular motion?
Speed in circular motion may be constant, but velocity will be changing because the direction is always changing, and direction just be considered as well as magnitude as velocity is a vector quantity
How can acceleration be described in relation to circular motion?
Because acceleration is defined as the rate of change of velocity, it can be described as accelerating due to the change of direction causing the change in velocity, even if speed is constant
Define centripetal force
The resultant force on an object, acting towards the centre of the circle, causing it to move in a circular path
How can frictional force cause an object to move in a circular path?
e.g. car travelling around a roundabout
Friction between the tyres on a turned wheel and the road acts inwards and provides the centripetal force to keep the car moving in a circle
How can gravitational force cause an object to move in a circular path?
e.g. satellite orbiting the Earth
Gravitational attraction between the satellite and the Earth provides centripetal force
Combination of this force and orbital speed of the satellite keeps it moving in a circle
How can electromagnetic force cause an object to move in a circular path?
e.g. electron orbiting nucleus of an atom
Electrostatic attraction between electrons and protons provides centripetal force which keeps it moving in a circle
How can the force of tension cause an object to move in a circular path?
e.g. rubber bung being spun around on a string
Force of tension in the string provides centripetal force, keeping the bung rotating in a circular path
Describe an experiment to investigate circular motion
Wear eye protection and work outside
Tie one end of string to a rubber bung and make a mark on the string at a distance of 0.30m from the bung
Attach a 1.0N weight at the other end of the string and whirl the bung in a horizontal circle (centripetal force on bung is 1.0N)
Adjust the speed of rotation so the radius of the circle is constant and equal to 0.30m and continue to whirl the bung at a constant speed
Measure time for 10 revolutions of the bung
Determine the speed of the bung using s = d / t and multiply by 10 as it is making 10 revolutions
Repeat with different values of centripetal force by adding masses to the string and keeping the bung whirling at the same radius
Record results in a table
Plot a graph of force against velocity squared and draw a straight line of best fit
Gradient is equal to mass / radius
Determine the mass of the bung from the gradient and the value of r used in the investigation
For the experiment that investigates centripetal force, what happens when the radius of the string is constant?
The weight on the bottom of the string does not rise or fall so it is in vertical equilibrium and the tension in the string equals the weight
Tension in string also provides the centripetal force that causes the bung to move in a circle
