Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

For a good viewof all the demosplease sit near

the front(ie front 5 rows)

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

BoomerangsBouncing Balls

andother spinning things

Dr Hugh Hunt

CambridgeUniversity

EngineeringDepartmentTrinity College Cambridge

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

Bouncing balls

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

Spinning and Rolling

the gyroscopic effect

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

The Gyroscopic Effect- Coffee grinder- Angle grinder

- Hair drier

For details go to www.hughhunt.co.uk

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

Circular motion

speed

mass

force string

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

Spin

FAST

Arms in,Feel Light

Spin

slowly

Arms out,

feel Heavy

1: ballet dancers and ice skatersMoment of Inertia J : “an Angular Mass”

Conservation of Angular Momentum J

JJ

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

2: pointing the Hubble Telescope

No spin

Still no spin !

Conservation of Angular Momentum J

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

3: spinning in space

Conservation of Angular Momentum J

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

The Gyroscopic effect

Couple

C

SPIN

(Angular momentum)

C = J

Precession

J = moment of inertia of wheel

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

How Wings Work

Air flowAir deflecteddownwards

V

Liftforce

F

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

BoomerangsPrecession

Directio

n of travel

faster

slower

more lift

less lift

Couple

Spin

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

Physics of boomerangs

4J

CLa4

where R = path radius

J = moment of inertia

= air density

CL = lift coefficient

a = size of boomerang

R = ________

flick-of-the-wrist

= boomerang spin

V = boomerang velocity

and a = 2 V

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

They make great christmas presents!

Boomerangs come in many shapes and sizes.

Hugh Hunt, Trinity College, Cambridge www.hughhunt.co.uk

The End

www.hughhunt.co.uk

Google: Hugh Hunt Boomerangs

Trinity College Cambridge www.trin.cam.ac.uk

Cambridge University Engineering Dept www.eng.cam.ac.uk