Gravity

The force not the movie

Forces• Force (N) is any influence that can change the

trajectory, speed or shape of a body.• Change in state of motion of a body• Distortion of a body

Forces

• A force is represented by a vector with both direction and magnitude

Forces applied…

• In the same direction as motion will cause an acceleration.

• In opposing direction to the motion will cause a decceleration of the object

• In perpendicular manner to the motion will cause a deviation of the object.

Forces

• If a force is applied– in the same direction as the motion of a body it

will accelerate

– in the opposite direction as the motion of a body it will decelerate

– Perpendicularly to the direction of motion of a body it will change trajectories

Forces

• An equilibrium of forces is achieved when the resulting force is equal to 0

• ***– Add forces in the same direction– Subtract forces in opposing direction

1. Weight vs. Mass

Definitions

MASS: measure of the quantity of matter in an object

WEIGHT: measure of the gravitational force acting on an object

Mass• Amount of matter an object has

• Measured in g or in kg

• Is measured by a balance

Weight• Pull that gravity exerts on

an object

• Measured in N

• Measured by a scale

• If the mass increases…

To recap:

• Mass and Weight are not the same

• Mass is the amount of matter• Weight is the gravitational pull on this matter

• Mass is measured in g or kg• Weight (being a force) is measured in N

• Mass and weight are proportional to one another

2. Calculating the gravitational Force

Fg = mg

Calculating the gravitational force

• Fg = mg– Where Fg = gravitational force or weight (N)

m = mass (kg)g = gravitational constant

• If an object has a mass of 30g what is its weight in Newtons on our planet?

• What if it was on Mars?

Astronomical Phenomenon

• Tides:– Gravitational effect of

the moon (and Sun) on the hydrosphere

Astronomical Phenomenon