Mass and WeightMass This is the amount of matter. (Kg)

Weight This is the force of gravity pulling on the mass. (N) * less on the moon , zero in deep space.

There is a very, small force of attraction between an apple and an orange.* too small to measure!

Weight vs. Mass

Earth’s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N.

W

gM

Weight = Mass x Gravitational Field Strength

(in N) (in kg) (in N/kg)

1) What is the weight on Earth of a book with mass 2kg?

2) What is the weight on Earth of an apple with mass 100g?

3) Dave weighs 700N. What is his mass?

4) On the moon the gravitational field strength is 1.6N/kg. What will Dave weigh if he stands on the moon?

Forces on falling objects

1. Object falling freely

Forces Acting Motion

Forces on falling objects

1. Object falling freely

Forces Acting Motion

the force of gravity (weight)

Uniform acceleration

Forces on falling objects

1. Object falling freely

Forces Acting Motion

the force of gravity (weight)

Uniform acceleration

Forces on falling objects

1. Object falling freely

Forces Acting Motion

the force of gravity (weight)

Uniform acceleration

Object in air

Forces on falling objects

1. Object falling freely

Forces Acting Motion

the force of gravity (weight)

Uniform acceleration

Object in air

Forces on falling objects

1. Object falling freely

Forces Acting Motion

the force of gravity (weight)

Uniform acceleration( …….. m/s/s)

Object in air

acceln = gradient

Forces on falling objects

1. Object falling freely

Forces Acting Motion

the force of gravity (weight)

Uniform acceleration( …….. m/s/s)

Object in air

acceln = gradient

Forces on falling objects

1. Object falling freely

Forces Acting Motion

the force of gravity (weight)

Uniform acceleration(10 m/s/s)

Object in air

If a 1kg mass is released above the ground

* the force of gravity on it is 10N* its acceleration is force = 10N =10m/s/s mass 1Kg

Forces on falling objects

1. Object falling freely

Forces Acting Motion

the force of gravity (weight)

Uniform acceleration(10 m/s/s)

2. Object falling through a fluid

Forces Acting Motion

force of gravity (weight)* initial acceleration (10 m/s/s)**

Object in air

2. Object falling through a fluid

Forces Acting Motion

force of gravity (weight)* initial acceleration (10 m/s/s)* decreasing acceleration to zero* terminal velocity

Drag force (air resistance)

Buoyancy (upthrust)

Object in air

2. Object falling through a fluid

Forces Acting Motion

force of gravity (weight)* initial acceleration (10 m/s/s)* decreasing acceleration to zero* terminal velocity

Drag force (air resistance)

Buoyancy (upthrust)

Object in air

Terminal VelocityConsider a skydiver:

1) At the start of his jump the air resistance is _______ so he _______ downwards.

Terminal VelocityConsider a skydiver:

1) At the start of his jump the air resistance is _______ so he _______ downwards.

2) As his speed increases his air resistance will _______

Terminal VelocityConsider a skydiver:

1) At the start of his jump the air resistance is _______ so he _______ downwards.

2) As his speed increases his air resistance will _______

3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL VELOCITY

Terminal VelocityConsider a skydiver:

4) When he opens his parachute the air resistance suddenly ________, causing him to start _____ ____.

5) Because he is slowing down his air resistance will _______ again until it balances his _________. The skydiver has now reached a new, lower ________ _______.

Velocity-time graph for terminal velocity…

Velocity

Time

Speed increases…

Terminal velocity reached…

Parachute opens – diver slows down

New, lower terminal velocity reached

Diver hits the ground

On the Moon

less than

equal to

equal to