6.1 - Circular Motion Flashcards
Is velocity a scalar or vector?
Vector.
Is acceleration a scalar or vector?
Vector.
What is uniform circular motion?
Motion in a circle at a constant speed.
What is happening to the speed, direction and velocity of an object in uniform circular motion?
An object in uniform circular motion has a constant linear speed
It is also constantly changing direction, meaning there is a constantly changing velocity.
What does it mean if an object has a constant speed but a changing direction?
It means there’s a constantly changing velocity, meaning the object must be accelerating.
What is centripetal acceleration?
The acceleration of an object towards the centre of a circle when an object is in motion (rotating) around a circle at a constant speed.
This is perpendicular to the direction of the linear speed.
In what direction does centripetal force and acceleration act?
Towards the centre of the circular path.
What is angular displacement defined as?
The change in angle, in radians, of a body as it rotates around a circle.
What is a radian defined as?
The angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.
What is the equation for angular displacement?
Δθ = Δs/r
Δs = length of the arc, or the distance travelled around the circle (m)
r = radius of the circle (m)
What is the conversion from degrees to radians?
θ° x π/180 = θ rad
What is the conversion from radians to degrees?
θ rad x 180/π = θ°
What is angular speed defined as? (⍵)
The rate of change in angular displacement with respect to time.
What is the equation to calculate angular speed?
⍵ = Δθ/Δt
Δθ = change in angular displacement (radians)
Δt = time intervals (s)
How else can angular speed be calculated? (using time period and frequency equation)
⍵ = v/r = 2πf = 2π/T
v = linear speed
r = radius of orbit
T = the time period
f = frequency
What are some equations for centripetal acceleration?
a = v²/r
v = linear speed
r = radius of the circular orbit
a = r⍵²
⍵ = angular speed
a = v⍵
What is centripetal force defined as? (F)
The resultant force towards the centre of the circle required to keep a body in uniform circular motion. It is always directed towards the centre of the body’s rotation.
How can you calculate centripetal force?
F = mv²/r = mr⍵² = mv⍵
m = mass
v = linear velocity
⍵ = angular speed
r = radius of the orbit
What is the unit for angular speed?
rad s⁻¹
What other force (other than centripetal) would be acting if a car is travelling around a roundabout?
Friction between car tyres and the road.
What other force (other than centripetal) would be acting if a ball is attached to a rope moving in a circle?
Tension in the rope.
What other force (other than centripetal) would be acting when Earth is orbiting the Sun?
Gravitational force.
