Dynamics Dynamics

The study of forces and energies

A force is a push or a pull that acts on an object.

It has a specific direction.It has a size or magnitude.

A force is a VECTOR !

How Do We Represent Forces?

Force = 100 N to the right

SI unit for force is NEWTON

SI unit for force is NEWTON

How Do We Represent Forces?

Force = 200 N to the right

Effects Of A Force On Motion

Effects Of A Force On Motion

Change the size and shape of objects

Make stationary objects to

move

Change the speed of a

moving body

Cause a moving body to change its direction of motion

Resultant Of Two More Forces

Two or more forces on a body can be replaced by a single force called the resultant force.

8

2

0

to the right

to the right

Balanced Forces And Unbalanced Forces

Balanced – Zero resultant force Unbalanced – there is a resultant force

Free-Body Diagram

Newton’s First Law Of Motion

Newton’s first law of motion states that an object will remain in a state of rest or uniform motion in a straight line unless acted upon by an external force.

When there is NO resultant force acting ona stationary object, it will remain at rest.

Total upward force equal to total downward force

When there is NO resultant force acting on an object moving with constant velocity, it will continue to move that constant velocity in a straight line.

Newton’s Second Law Of Motion

Newton’s second law of motion states that the net force acting upon an object is equal to the product of the mass and acceleration of the object.

Force = Mass x AccelerationF = ma

Friction

Friction is a force that opposes the sliding motion between two surfaces in contact with each other.

Frictional Force

• Depends on the material in contact. • Depends on the roughness of the surfaces.• Is proportional to the force pressing the

surfaces together.• Is independent of the area of contact.

Positive Effects Of Friction

• Enable us to walk without slipping.• Used in brake pads to slow down

the motion of vehicles.• To pick up things such as using

chopsticks to pick up food.

Negative Effects Of Friction• Cause wear and tear of

moving parts in machines, motors and engines.

• Reduce the efficiency of engine power of cars by up to 20 %.

Ways To Reduce Friction• Using ball bearings or wheels.• Using lubricants such as oil and grease.• Use highly polished surfaces for moving

parts.

Ways To Reduce Friction• Designing the shape of the vehicle to be

streamlined.• Use air-cushion.