Chapter 3.2 & 3.3

Forces and Energy!!

Force

• Force is a push or a pull on an object!

• Forces can change the shape or motion of an object!

Force

• Lets recap!• What is acceleration?• It is a change in motion!!!• What causes acceleration?

• It is caused by a Force!

Types of Forces!

• Frictional Force• This is a force that

opposes motion.

Types of Forces!

• Gravitational Force• Gravity is a force that all

objects exert on each other.

• Newton’s Law of Universal Gravity states that all objects in the universe will attract other object with a force known as gravity!

Types of Forces!

• The unit of the measurement of gravity (weight) is the Newton (N).

• In the US we use the pound.• The relationship between

the masses of objects and the pull they have is directly related to the size of the mass!

• A bigger mass (like a star) has more gravity than a pencil!

Types of Forces

• Gravity is also inversely related to the square of the distance between the two objects.

• In other words…the farther apart they are, the less the force of gravity.

Newton’s Laws of Motion

• In order to understand Newton’s laws of motion, we first have to understand “Inertia”.

• Inertia is a property of matter whereby all matter resists change in its motion!

• If an object is at rest, it “wants” to remain at rest.

• If an object is in motion, it “wants” to remain moving!

Inertia

• For example:• A football will sit until it is thrown or kicked.• Once thrown or kicked, the football will keep

moving until something (like the ground) stops it!

• Forces are the agents causing changes in motion.

Newton’s First Law of Motion

• The first law of motion is based on the principle of inertia: the velocity of an object is not changed unless acted on by an outside force.

• This principle is equally true of objects in motion and objects at rest.

Newton’s Second Law of Motion

• This second states that an object accelerates in the direction of the applied force.

• It also states that the acceleration is directly related to the force and inversely related to the mass.

• There is an equation that shows this relationship:

a = F/mor

F = ma

Newton’s Third Law of Motion

• The third law states that: For every action there is an equal and opposite reaction.

• In other words, forces come in pairs…• Push on a wall, it pushes back on you…• Push on a basketball, it pushes back on you!

Newton’s Third Law of Motion

• Action/Reaction is why rockets get lift as they thrust off the ground.

Solids in a Circular Motion

• Objects move in a circular path.

• When an object swings around from a fixed string, the direction of the motion keeps changing.

• This pull keeps the weight from moving in a straight line.

• This is a force called centripetal force.

Centripetal Force

• The word centripetal means “to seek center”

• It is a force that causes an object to move in a curved path rather than a straight path.

Centrifugal Force

• Centrifugal force is the force that acts in the opposite direction of the pull on the object.

• It is the pull of the object on the fixed location of the string.

• Without centripetal force, centrifugal force cannot exist.

Gravity

• Gravity is a centripetal force that keeps the planets from continuing in a straight path away from the sun.

Energy for Movement

• Energy in the scientific sense is the ability to do work.

• Work is only done when a force is applied and an object moves in the direction of the force applied.

• We can experience and observe the effects of energy on matter and hear sound energy.

Mechanical Energy

• Matter in motion or with potential of motion possesses Mechanical Energy.

• Energy is always conserved!!!• Energy changes form from one type of energy

to another, but it is never “LOST”.

Mechanical Energy

• There are many types of energy!!!– Electrical Energy– Chemical Energy– Heat Energy– Sound Energy– Nuclear energy

– These are just some!!!

Energy of Motion!!

• Mechanical Energy can be classified as either Kinetic or Potential.

• Kinetic Energy is Energy in Motion• Potential Energy is Energy of Position, or

Condition, or it is known as Stored Energy!

Tackle This!!!

• Turn to page 118 in your books!• Answer the Tackle This Questions!!!

• You can answer this next to your page of notes!