FORCES

What is a force?

• A force is a PUSH or a PULL.• Forces do not have mass nor do

they occupy a space.• Forces can

– tear, bend, twist, or stretch an object.– Change the direction of the motion

• Measured in Newtons (N)

2 main types of forces

• Contact forces– A force between two objects in direct contact

with one another.Frictional

• Non-Contact forces– Forces that can act on objects at a distance

and between two objects which are not in direct contact with one another.

MagneticGravitational

Gravitational Force

• Pulls objects towards the center of the earth• Objects exert a force of attraction on all objects

around it.– The force may be small that we can’t feel it.

• The larger the mass, the stronger the gravitational force– The sun’s gravitational force pulls smaller bodies

towards it

• The closer the two objects are, the stronger the gravitational force

Gravitational force

• Objects fall to the ground at the same rate, regardless of their mass in the absence of air

• Overcoming gravity:– Energy is needed to overcome gravity– More energy if you’re going against it– Less energy if you’re going towards it.

Gravitational energy in our daily lives

Frictional Force

• A force that opposes motion. • Produced when two surfaces are in

contact with each other• Can cause an object to move slower• More friction is exerted if the object’s

mass is great• Surfaces play a role in the amount of

friction generated

Frictional Force

• Types of friction– Sliding

• Two solid objects with one object sliding over the other• snowboarding

– Rolling• When a circular object rolls over a surface• cycling

– Fluid• Involves a solid object moving through a wet or fluid (liquid or

gas)surface• Parachuting, wakeboarding

Infer the friction generated in the given

pictures

Frictional energy

• Energy is required to overcome friction.• How much energy is needed to

overcome friction over smoother surfaces?

• How much energy is needed to overcome friction over rougher surfaces?

• When is frictional energy beneficial? When is frictional energy harmful?

Frictional energy in our lives

Magnetic Force

• A force of attraction that pulls unlike poles.

• A force of repulsion that pushes like poles.

• A MAGNET attracts magnetic materials, which include those made up of Iron, steel, cobalt and nickel

Magnetic force

• A stronger magnet exerts a stronger force of attraction– The material may move faster– A stronger force is needed to

overcome a stronger magnet

N S N S

Magnetism in our daily lives

The PENDULUM

String

Metal ball

gra

vity

The PENDULUM

• Found in clocks; has a weight and a string

• Air resistance (frictional force) and gravity affect the motion of the pendulum

• The length of the string also affects the time for the pendulum to complete its swings