Falling downFalling downPhysics On the Road

Lesson 8

LI…Describe free fall.Use kinematic equations to

make predictionsExplain parabolic projectile

motion.

Free fall

Gravity is uniform acceleration

Galileo first proposed the idea that all objects fall with uniform acceleration.

He proved it by rolling balls down slopes

It is an idea with far reaching implicationsGravity accelerates all

objects on Earth at a rate of 9.8 ms-2

Air resistance

Why doesn’t it look like all objects fall at the same rate.

Gravity is not the only force acting.

Air resistance acts against motion.

The air resistance depends upon size, shape but mostly speed.

Falling down Describe a parachute jump using a

velocity time graph.

time

velo

city

Still falling down Explaining a parachute jump Use the idea of forces

time

velo

city

w

w

w

f

w

f

w

f

Ignore air resistance - constant acceleration

∆v

∆t

∆t

t=0

2∆v

If you ignore air resistance falling objects gain speed at the same rate.They accelerate at Earth at a rate of 9.8 ms-2.

Q1. How far will a coin fall in 5 seconds?

0 ms-1

9.8 ms-1

19.6 ms-1

Sideways makes no difference

∆v

∆t

∆t

t=0

2∆v

0 ms-1

9.8 ms-1

19.6 ms-1

∆v

2∆v

9.8 ms-1

19.6 ms-1

Changing velocity in a parabolic path -vectors

v

∆v

v

v v

v

v

Due to gravity

v∆v

newv

v

∆vnewv

Demonstrate Your Understanding

Explain why this trick is not as dangerous as it looks.

EXTENDED ANSWER TASK

Use diagramsUse principlesUse vectorsUse calculations