# Forces Change Motion Force- push or a pull

## Presentation on theme: "Forces Change Motion Force- push or a pull"— Presentation transcript:

Forces Change Motion Force- push or a pull
Can speed up or slow down the motion of an object or change its direction without changing its speed.

Have a size and direction
Forces are VECTORS Have a size and direction

Balanced Forces Ex: Physics book at rest on a table top.
Two forces are acting upon the book. Gravity pushes down on the book. The table pushes up on the book Both forces are equal in size/magnitude/number and opposite in direction

Balanced Forces- The forces are balanced
The book is said to be at equilibrium. No unbalanced force acting upon the book When all the forces acting upon an object balance each other, the object will be at equilibrium; it will not accelerated.

Balanced Forces A person standing upon the ground.
Two forces acting upon the person. Gravity exerts a downward force. The floor of the floor exerts an upward force.

Balanced Forces These two forces are of equal magnitude/size
In opposite directions They balance each other. The person is at equilibrium. There is no unbalanced force acting upon the person

Balanced vs. Unbalanced Forces
Net Force- The overall force acting on a object when ALL the forces are combined If the NET FORCE is ZERO all of the forces acting on the object are zero.

Balanced vs. Unbalanced
BALANCED forces are the same as having no force at all. The motion of an object doesn’t change

Change the motion of an object
Unbalanced Forces Change the motion of an object

Balanced vs. Unbalanced
If one of the basketball players pushes with a grater force than the other player, the ball will move in the direction that player is pushing. The motion of the ball changes because the forces on the ball are UNBALANCED.

Balanced forces Don’t change an object’s speed or direction
A unbalanced force is needed to change an object’s motion

Sir Isaac Newton lived during the 1600s
His laws of motion explain: Rest Constant motion Accelerated motion Describe how balanced and unbalanced forces act to cause these states of motion.

Sir Isaac Newton Built his ideas on Galileo Galilei’s ideas
Newton’s 3 Laws of Motion

Newton’s First Law Object at rest remains at rest, and objects in motion remain in motion with the same velocity, unless acted upon by an unbalanced force.

Newton’s First Law The ball is in motion with the same velocity, unless acted upon by an unbalanced force.

Have you ever been riding in a car when the driver suddenly slammed on the brakes?
How did your body move as the car came to a stop? You probably felt your body move forward..

When you felt this happening you experienced Newton's first law of motion.
Newton's first law of motion says that an object in motion will stay in motion and an object at rest will stay at rest unless acted on by an unbalanced force

Newton called his first law inertia.
In the car your body was in motion, traveling at the same speed as the car. When the car stopped, your body stayed in motion. If you were not wearing a seatbelt and you were traveling very fast, your body could continue to move forward through the windshield!

Try the following activity to demonstrate this law!
Place a 3x5 card on top of a glass. Put a coin on the center of the card. Flick the card horizontally with your finger. What happens to the coin? Explain what happened to the coin using Newton's first law.

Inertia Resistance of an object to change in the speed or direction of its motion Newton’s first law When you measure the mass of an object you are also measuring its inertia It is easier to push or pull an empty box than the same box when it full of books

Main Ideas Objects tend to stay at rest unless something hits them.
Things keep on doing what they are doing unless something hits them. Inertia- the name given to an object’s tendency to keep doing what it is doing

Force Mass x Acceleration F= m x a Units are Newtons (N) kg x m/s2

Newton’s 2nd Law The acceleration of an object increases with increased force Decreases with increased mass Is in the same direction of the force

Newton’s 2nd Law- Ties Together- Force, Mass, Acceleration
Acceleration of an object depends on the mass of the object and the size of the force applied If an object loses mass, it can gain acceleration if the force remains the same

Newton’s 2nd Law Acceleration of an object increases with INCREASED FORCE and decreases with INCREASED MASS. The direction in which an object ACCELERATES is the same as the direction of the force.

Newton’s 2nd Law Who is exerting the most force behind the cart?

Newton’s 2nd Law Which cart has the largest mass?
Which is the easiest to push?

Main Ideas- Newton’s 2nd Law
Small mass leads to LARGE acceleration Large mass leads to SMALL acceleration

A net force acting on an object causes the object to accelerate.
Main Ideas A net force acting on an object causes the object to accelerate. A net force acting on an object causes an object to accelerate.

Centripetal Force Any force that keeps an object moving in a circle
This force points toward the center of the circle Without this force object would go flying off in a straight line Centripetal force keeps the planets in orbit

Spinning stuff- Centripetal Force
Spinning a bucket of water over your head without spilling a drop, you are also applying a centripetal force. If you let go of the bucket, it will move in a straight line Centripetal force is always directed at the centre of an object.

Centripetal Force

Centripetal Force Greater acceleration = greater centripetal force
More mass requires more centripetal force to have the same circular speed as a less massive object. No matter the mass of an object, if it moves in a circle, its force and acceleration are directed to the center of the circle

Newton’s 3rd Law For every action, there is an equal and opposite reaction Action and Reaction Forces Rockets going into space Squid and Jellyfish movement

Types of Forces Contact Gravity Friction

Types of Forces Contact Force- when one object pushes or pulls another object by touching it, the first object is applying a contact force to the second.

Balanced Forces vs. Action/Reaction Forces
Balanced Forces act on a single object Action and Reaction Forces act on DIFFERENT objects

What are examples of contact forces?

Momentum Found in moving objects Measure of mass in motion p= mv
momentum = p m= mass v= velocity Units kg x m/s

Momentum More mass= more momentum Momentum depends on mass
Momentum takes into account velocity Is a vector (has size and direction)

Collision Two objects in close contact exchange energy and momentum

Conservation of Momentum
Total momentum of a system of objects do not change, as long as no outside forces are acting on that system To find total momentum of objects moving in the SAME direction, add the momenta of the objects. Objects traveling in opposite directions, subtract the momentum from one another.

Bibliography slide

Types of Forces The ground produces a CONTACT FORCE on the skater as she pushes against the ground. GRAVITY pulls the skater down Friction between the skates and the ground

Gravity Force of attraction between two masses
Earth’ s gravity is pulling on the skater, holding her to the ground The force of gravity depends on the mass of the objects.

FRICTION Force that resists motion between two surfaces that are pressed together.