# Gravity and Circular Motion RevisionPage 1

#### WATCH ALL SLIDES

Slide 1 Gravity and Circular Motion Revision AQA syllabus A Section 13.3.1-6

B.W.Hughes

Slide 2 ## Circular motion

When an object undergoes circular motion it must experience a

centripetal force

This produces an acceleration

towards the centre of the circle

Slide 3 Angular Speed

Centripetal Force

Slide 4 Slide 5 Slide 6 Slide 7 ## Angular speed

Angular speed can be measured in ms-1 or

Revs-1 (revolutions per second)

The symbol for angular speed in radians per second is

ω

Slide 8 ## Converting to ω

To convert v to ω

ω = v/r

To convert revs per second to ω

Multiply by 2π

Slide 9 Acceleration

The acceleration towards the centre of the circle is

a = v2/r OR

a = ω2r

Slide 10 ## Centripetal Force Equation

The general force equation is

F = ma

so the centripetal force equation is

F = mv2/r OR

F = m ω2r

THESE EQUATIONS MUST BE LEARNED!!

Slide 11 ## Example

Gravity provides the accelerating force to keep objects in contact with a humpback bridge. What is the minimum radius of a bridge that a wheel will stay in contact with the road at 10 ms-1?

v = 10 ms-1, g = 10 ms-2, r = ?

a = v2/r = g so r = v2/g

r = 102/10 = 10 m

Slide 12 ## Newton’s Gravitation Equation

Newton’s Gravitation equation is

F = -Gm1m2/r2

MUST BE LEARNED!!

Negative sign is

a vector sign

G is

Universal Gravitational Constant

Slide 13 m1 and m2 are

the two gravitating masses

r is

the distance between their centres of gravity

The equation is an example of an

Inverse square law

Slide 14

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