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How things move and the forces that act on them.

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In science, force, a push or a pull.

Think of a game of bowling.The moving object - the

ball, exerts a pushing force against anything it hits - the

ten pins.

What is a What is a Force?Force?

Think of tugging on a rope.

The person in the picture is exerting a pulling force on his end of the rope.

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Characteristics of ForcesCharacteristics of Forces1. We cannot see forces.  

• sometimes feel the effects they have on things. 

• the balloons are affected by forces.

2. Forces can make things speed up. 

• hit a tennis ball and it speeds up. 

3. Forces can make things slow down or stop.  • A parachute can make an object

slow down because of air resistance. 

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4. Forces can make things change direction and goes in the direction the force is

applied. • ball changes direction by hitting it with a bat. 

Characteristics of ForcesCharacteristics of Forces

5. Forces can make things change shape. 

• squeeze or kick a soccer ball, it will be compressed. 

6. Forces can make things turn.

• use a wrench to loosen or tighten a nut. 

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Connecting Forces with MotionConnecting Forces with MotionSometimes forces are obvious……..

Sometimes forces are NOT as obvious……..

…moving car crashing into a stationary tree.

…Can you feel the force the ground exerts on your feet?

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http://www.youtube.com/watch?v=43VoMesUd2Q

Tornado Destruction

http://www.youtube.com/watch?v=TRDpTEjumdo

Killer Tsunami

http://www.youtube.com/watch?v=aWEZI1Q6xj0

Hurricane Ike

Nature’s ForcesNature’s Forces

http://www.youtube.com/watch?v=5hE2DZdl0IA

Active Volcano

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1. Balanced Forces –

• forces of the objects are equal in size and opposite in direction

• when things are NOT moving

Types of ForcesTypes of Forces

Example:Gravity pulls the table down,but the table is pushed up by the floor that it stands on…so the table does not move and the forces are balanced.

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2. Unbalanced Forces -• forces of the objects are NOT equal in size or direction• changes movement and direction

Example 1:

The hurdler has lost contact with the ground and has moved upwards. The earth’s pull is unbalanced. This makes him slow down and change direction, so he can come down to earth again.

Example 2:

The seesaw is unbalanced because the forces are not equal.

Types of Forces - ContinuedTypes of Forces - Continued

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3. Net Forces – • sum of the forces on an object changes the speed or direction or both.Upward Force 245N + 245N = 490N

Downward Force = 490N

Net Force = 490N Up- 490N Down

0 N because the difference between the upward force and the downward force is equal to zero.

What happens to the person on the swing?

Types of Forces - ContinuedTypes of Forces - Continued

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Net Forces – Another Example

The man is pushing with 100N and the woman is pushing with 100N.

So what will happen to the car?

What is the net force?

The car is pushing back with a force of 250N.

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4. Gravity -

Think what happens to ripe fruits such as apples that grow on trees…

They will fall to the ground unless they are

picked first.

         

  

Types of Forces - ContinuedTypes of Forces - Continued

•Pull of gravity is dependent on 2 things

• Force exerted by every object in the universe on every other object

1. MASS of the object

2. DISTANCE between the objects

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5. Weight - • measure of the force of gravity on an object.• changes depending on the amount of GRAVITY

• NOT the same as MASS

• Measured in NEWTONS (N) with a Spring Scale

Types of Forces - ContinuedTypes of Forces - Continued

Example:The Earth is LARGER in size compared to the Moon so the Earth will have a LARGER pull of gravity so it will have more weightYou could weigh 200 Pounds on Earth, but 175 Pounds on the Moon.

• Mass Stays the Same, there is no effect of gravity• So if you have a MASS of 100kg on Earth you will have a MASS of 100kg on the Moon

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6. Buoyant Force - • Upward force exerted by a fluid that pushes an

object up • makes it seem to lose weight in a fluid.• (a fluid means a liquid or a gas).

Example 1:The buoyancy, keeps ships afloat.

Types of Forces - ContinuedTypes of Forces - Continued

Example 2:The warm air convection currents keep the balloon buoyant. 

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7. Magnetic Force / Electrical Force

• Force between positive and negative charges

Types of Forces - ContinuedTypes of Forces - Continued

Example 1:

The negative (-) ATTRACTS to positive (+)

Like ends -/- and +/+REPEL each other

Example 2:

Atoms release light photons when their electrons become excited. Electrons are the negatively charged particles that move around an atom's nucleus (which has a net positive charge).

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8. Nuclear Force

• Force that holds the nucleus of an atom together.

Types of Forces - ContinuedTypes of Forces - Continued

• The protons in the nucleus of the atom are positively charged. If protons interact, they are usually pushed apart by the electromagnetic force. • However, when two or more nuclei come VERY close together, the nuclear force comes into play. • The nuclear force is a hundred times stronger than the electromagnetic force so the nuclear force may be able to "glue" the nuclei together so fusion can happen.

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9. Centripetal Force• Force that moves in a circular motion

Examples

Amusement Park Rides and Satellites that orbit the Earth

Types of Forces - ContinuedTypes of Forces - Continued

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10. Friction

There is friction between a car tire and the road with which it is in

contact. 

• Resistance between two surfaces that contact each other. • Without friction, you wouldn’t be able to walk, hold things, or keep your shoelaces tied.

• Effects of Friction can be lessened with lubricants such as oil and grease.

• Amount of Friction depends on 2 things:

1. Kinds of surface2. The force pressing the surface together

• Friction generates heat, thus slowing objects down

Types of Forces - ContinuedTypes of Forces - Continued

18Question 1: Would you expect more friction between an oily floor and a slick, leather shoe sole or between a rough sidewalk and the bottom of a tennis shoe?

Question 2: How do you think friction helps

us in our everyday lives?

Question 3: Why is it important to have the tires on our cars inflated to the proper level?