Free Fall & ProjectilesFree Fall & Projectiles

Chapter 3, sections 7-9 & Chapter 8, sections 1-4Chapter 3, sections 7-9 & Chapter 8, sections 1-4

Free Fall

The acceleration of gravity (g) for objects in free fall at the earth's surface is 9.8 m/s2.

Galileo found that all things fall at the same rate.

Free Fall

The rate of falling increases by 9.8 m/s every second.

Height = ½ gt2

For example:

½ (9.8 )12 = 4.9 m

½(9.8)22 = 19.6 m

½ (9.8)32 = 44.1 m

½ (9.8)42 = 78.4 m

Free Fall

• A ball thrown horizontally will fall at the same rate as a ball dropped directly.

• Horizontal and Vertical Forces are INDEPENDENT of each other

Free Fall

A ball thrown into the air will A ball thrown into the air will slow down, stop, and then slow down, stop, and then

begin to fall with the begin to fall with the acceleration due to gravity. acceleration due to gravity.

When it passes the thrower, it When it passes the thrower, it will be traveling at the same will be traveling at the same rate at which it was thrown.rate at which it was thrown.

Free Fall

An object thrown upward at an angle to the ground follows a curved path called

a parabola.

Projectile Motion

Projectile: a body in free fall that is subject only to the forces of gravity and air resistance

Bodies projected into the air are projectiles.projectiles.Examples of moving body as projectile:• Shot putt• High jumper• Long jumper• Soccer ball• Baseball• Ski jumper

Projectile Motion

• The ball is in free fall vertically and moves at constant speed horizontally!!!

Projectile Motion

Projectile Motion

• There is NO acceleration horizontally!!!

• Gravity results in a horizontal acceleration as the cannonball drops to the ground.

Air Resistance

• In air…– A stone falls faster

than a feather• Air resistance

affects stone less

• In a vacuum– A stone and a

feather will fall at the same speed.

Air Resistance

• Free Fall– A person in free

fall reaches a terminal velocity of around 54 m/s

– With a parachute, terminal velocity is only 6.3 m/s

• Allows a safe landing

Air Resistance

• Ideal angle for a projectile– In a vacuum, maximum distance is at an angle of 45o

– With air resistance (real world), angle is less• Baseball will go furthest hit at an angle of around 40o