Ch. 13 Force and Motion

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# Ch. 13 Force and Motion - PowerPoint PPT Presentation

Ch. 13 Force and Motion. How can you describe motion?. Types of motion: constant (Earth) vibrational (guitar string) variable (cars, trucks) circular (car tire) periodic (pendulum). Speed and Velocity. Average speed = divide Distance and Time

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### Ch. 13 Force and Motion

How can you describe motion?
• Types of motion:
• constant (Earth)
• vibrational (guitar string)
• variable (cars, trucks)
• circular (car tire)
• periodic (pendulum)
Speed and Velocity
• Average speed = divide Distance and Time
• Velocity – Describes the speed and direction of an objects motion (D/T)
• Point of reference is a set location against which motion is measured.
Find the speed

The monorail at Disney moved 100 meters in 20 seconds. What is the average speed?

100 m =

What are forces?
• The magnitude of force is measured in Newtons (N).
• Forces have both magnitude and direction.
• Examples of Earths gravitational pull are:
• An apple falling from a tree
• Jumping up and coming back down
• Satellite orbiting around Earth
• Pendulum swinging back and forth
Magnetism and Electricity
• Magnetism – Force that pushes and pulls objects
• The cause of a magnetic force is the magnetic field of an object.
• Magnetic forces are greatest at a magnets poles.
• Electric forces act between objects that are electrically charged.
• The cause of an electric force is objects gaining or loosing electrons.
Examples of Magnetic and Electric forces

Magnetic

Electric

Rubbing a balloon against your hair will create enough

static charge to make the balloon ‘stick’ to a wall.

• A compass detects the Earth’s magnetic field. A needle is moved by the magnetic force, so that one end points north and the other end points south.
Friction
• Friction slows, stops, or prevents anything from moving.
• Shape, speed, or texture of an object can affect the amount of friction with another object.

**In space there is less friction than Earth. This means that a satellite moving around Earth will not slow down much.

Work and Power
• Work is measured in Joules (J)
• Power is measured in Watts (W)
• Examples of forces: gravity, electrical forces, friction, or magnetism.
• An example of an electric force is paper clinging to a comb.
Newton’s Laws of Motion
• The net force of an object is the combination of all forces on an object.
• Forces can be balanced or unbalanced.
• An object is in a state of equilibrium when all forces acting on it balance each other out.
• If an object is motionless it will remain motionless because all forces acting on it balance each other out.
Newton’s First Law

An object in motion stays in motion

and

An object at rest stays at rest

unless

A net force acts on the object.

Inertia
• Inertia is the amount of resistance an object has to change in motion.
• A moving object with a lot of inertia will require a greater force to stop and it will be harder to start than an object with less inertia.
• Ex. Your body rises out of the seat on a roller coaster ride
Newton’s Second Law

The acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object.

The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object.

• The stronger the force, the greater the acceleration.
• Ex. When someone pushes a box across the classroom floor, they exert a force. This force causes the box to accelerate and move.
Newton’s Third Law

**The action-reaction law of motion.

When an object exerts a force on another object, the second object exerts a force on the first object.

Ex. Person leaning on a wall, hammer pounding a nail into a board

• Always occur in pairs because the forces are always equal and opposite.
All 3 laws in use

Scenario: A satellite orbiting Earth is knocked out of its orbit by a meteor

1st law: Satellite remained in orbit because an object in motion stays in motion.

2nd law: The force of the meteor caused a change in the motion of the satellite.

3rd law: The force of the meteor hitting the satellite is equal and opposite to the force of the satellite hitting the meteor.

Simple Machinesmake work easier

Wheel and axle

-Door knob

-Steering wheel

Pulley

-Flag Pole

Lever

-See-saw

-Clothes pin

Inclined Plane

-Ramp

-Door stop

Complex Machines
• Uses 2 or more simple machines
• Use forces such as: gravity, magnetism, human force, burning fuel, or electricity.

Ex. Go cart, sailboat, screw, car engine, airplane

Why a screw?

It consists of metal rod with an inclined plane wrapped around it, and changes direction and the amount of force needed.