Summary A-LEVEL PHYSICS NOTE

PHYSICS A2
CHAPTER 12 : MOTION IN A CIRCLE

12.1 Kinematics of uniform circular motion
● define the radian and express angular displacement in radians
● understand and use the concept of angular speed


TERMS DEFINITION/ FORMULA

Angular - Change in angle of a body
displacement - as it rotates around a circle

Radian - Angle subtended at the centre of a circle
- by an arc of length equal to the radius of the circle

Angular velocity - Rate of change of angular displacement
- swept out by radius

Angular speed 1. string:
- Rate of change of angle
- by the string
2. ball :
- Change in angular displacement
- per unit time

● Relationship between v, r and ω




- ω : angular velocity / angular frequency




1

,12.2 Centripetal acceleration
1. understand that a force of constant magnitude that is always perpendicular to the
direction of motion causes centripetal acceleration
2. understand that centripetal acceleration causes circular motion with a constant
angular speed recall and use a = rω2 and a = v2 / r
3. recall and use F = mrω2 and F = mv2 / r
4. recall and use ω = 2π / T and v = rω


TERMS DEFINITION/ FORMULA

Centripetal force - Force that is always directed towards the centre of the
circle
- and at right angles to the velocity of the body

Centripetal - Acceleration that is always directed towards the centre of
acceleration the circle

Revolution - A type of circular motion where the object moves around a
fixed centre point called the axis of revolution




● Effects of centripetal force :
- The force can indeed accelerate the object
- by changing its direction, but it cannot change its speed
- direction of the acceleration is inwards

● Centripetal force vs Centrifugal force


Centripetal force Centrifugal force

Force required for circular motion Force that makes something flee from the
centre

Toward the centre Away from the centre




2

,● Derivation of formulae


∆𝑣 𝑣∆𝑠
𝑎 = ∆𝑡
= 𝑟∆𝑡

∆𝑠 = 𝑎𝑟𝑐 𝑙𝑒𝑛𝑔𝑡ℎ = 𝑟∆θ
∆θ
𝑎 = 𝑣 ∆𝑡
= 𝑣ω

𝑎 =𝑣ω
𝑣 = ω𝑟
2
𝑎=ω 𝑟


𝐹 = 𝑚𝑎
2
𝑎=ω 𝑟
2
𝐹 = 𝑚ω 𝑟


2π
ω= 𝑇
ω = 2π𝑓




3

, CHAPTER 13 : GRAVITATIONAL FIELDS
13.1 Gravitational field
● understand that a gravitational field is an example of a field of force and define
gravitational field as force per unit mass
● represent a gravitational field by means of field line

TERMS DEFINITION/ FORMULA

Gravitational fields - Region of space of are/volume
- where a mass experiences gravitational force

Gravitational field strength - Force per unit mass


● Gravitational field lines
- Direction of gravitational field : radially inwards
- Lines of equal field strength
- uniform gravitational field (i.e on Earth’s surface)
- parallel field lines




13.2 Gravitational force between point masses
● understand that, for a point outside a uniform sphere, the mass of the sphere
may be considered to be a point mass at its centre
● recall and use Newton’s law of gravitation F = Gm1m2 / r2 for the force between
two point masses
● analyse circular orbits in gravitational fields by relating the gravitational force to
the centripetal acceleration it causes
● understand that a satellite in a geostationary orbit remains at the same point
above the Earth’s surface, with an orbital period of 24 hours, orbiting from west to
east, directly above the Equator




4