# FORCES AND FRICTION.

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FORCES AND FRICTION

Bellringer #6

Bellringer #7 A force is: a. Anything that is in motion. b. Any push or pull on an object. c. Anything that reacts with another object. Motion is a result of: a. Any force, balanced or unbalanced. b. Only balanced forces. c. Only unbalanced forces. Friction is a result of: a. Two objects rubbing against each other. b. Tiny hills and valleys on the surface of object rubbing together. c. Both A and B Forces always act in pairs: a. True b. False

BELLRINGER READ THE FIRST PARAGRAPH ON PAGE 11 OF YOUR BOOK. THINK ABOUT OTHER WAYS YOU HAVE HEARD THE WORD FORCE USED.

THERE IS A BIG RELATIONSHIP BETWEEN FORCE AND MOTION
WHAT IS A FORCE? A force is simply a push or a pull. THERE IS A BIG RELATIONSHIP BETWEEN FORCE AND MOTION WITHOUT A FORCE THERE WOULD BE NO MOTION

FORCES ALWAYS OCCUR IN PAIRS
Force gives an object the energy to move, stop moving, or change direction.

Examples of forces acting on objects would be:
A flag being blown by the force of the wind. A jet engine propelling an airplane forward. Iron being pulled toward a magnet.

HOW DOES FORCE CAUSE MOTION?
Motion is a result of UNBALANCED FORCES. UNBALANCED FORCE is the total force on an object in one direction .

REMEMBER: Forces always come in pairs.
HOW DO UNBALANCED FORCES CAUSE MOVEMENT? REMEMBER: Forces always come in pairs. 2 Unbalanced forces acting in the same direction get added together and cause motion.

EXAMPLES OF UNBALANCED FORCES
PUSHING A SHOPPING CART SKIING DOWNHILL

WHAT IS A BALANCED FORCE?
Balanced Forces cause no motion. The paired forces occur in opposite directions and are of equal force.

EXAMPLES OF BALANCE FORCE
Two dogs of equal strength playing tug of war Skier on a flat surface

LET’S PRACTICE

WHICH PICTURES SHOW BALANCED FORCE?
WHICH PICTURES SHOW UNBALANCED FORCE?

Friction - The force that opposes motion between two surfaces.
FRICTION : FORCE THAT OPPOSES MOTION Friction - The force that opposes motion between two surfaces. Friction occurs because the surface of any object is rough. All surfaces are covered with microscopic hills and valleys. When surfaces touch, the hills and valleys of one surface stick to the hills and valleys of the other surface. This causes friction even if the surfaces look smooth.

All of these questions deal with friction !!!!!
Would you rather catch a ball diving in the grass or on concrete? Why do ice skates only have a small blade? Why put oil in your car? Why can’t you open a jar with lotion on your hands? All of these questions deal with friction !!!!!

FACTORS THAT AFFECT THE AMOUNT OF FRICTION
1. Roughness - The more rough the surface; more friction created. 2. Force - The more force pushing the object; the more friction between valleys. 3. Attraction between objects(static) - The greater the attraction; the more friction created.

Humans have tiny ridges in their hands and feet which increase the amount of friction. This allows us to clasp objects and avoid slipping. Tires are designed to increase friction on the road. HOW DO THEY DO THIS?

The rougher the surface the friction, ____________ because ______________________.
If the force is increased, the hills and valleys of the surfaces can come closer contact so friction is _______________. Less massive objects exert less force on surfaces than more massive objects so friction is less.

TYPES OF FRICTION 1. Sliding Friction 2. Rolling Friction 3. Fluid Friction

SLIDING FRICTION Definition - Friction caused by objects sliding across one another. Examples - Pushing an object (dresser), sledding, brakes, chalk

ROLLING FRICTION Definition - Friction produced by objects such as wheels or ball bearings. Examples - Wheels are placed under objects to reduce sliding friction. Cars, moving large objects with dollies,

FLUID FRICTION Definition - Force exerted by a fluid(gas and liquids).
Examples - Water, oil, and air. Sliding friction is usually changed to fluid friction by adding lubricants. Why is it on a slick floor?

STATIC FRICTION Definition - When a force is applied, but the object does not move. Examples - Block and a table. Block will move when the force is large enough to overcome the friction.

WAY FRICTION IS HELPFUL
1. Push against car to make it move. 2. Brakes to stop objects. 3. Between pencil and paper. 4. Friction between floor and feet.

WAYS FRICTION CAN BE HARMFUL
1. Friction in the engine causes temperature to rise. 2. Wind and water causes erosion. 3. Holes in you jeans. 4. Hard to move heavy objects.

WAYS TO REDUCE FRICTION
1. Lubricant(liquid or gas) 2. Wheels 3. Ball bearings 4. Make surfaces that rub against each other smoother.

WAYS TO INCREASE FRICTION
1. Make surface rougher(sand on ice or batters glove). 2. Increase the force pushing the surfaces together.

Name the different types of friction. Give examples of each.

Name two ways friction is helpful and harmful.

Name two ways to overcome friction.

Gravity, Free Fall, and Air Resistance
Gravity - the force that pulls objects toward one another. Free Fall – when only gravity is acting on an object. This is rare because of air resistance. All objects free fall at a rate of 9.8 m/s. A golf ball and basketball will hit the ground at the same time. Air Resistance – type of fluid friction which increases with the surface area of the object.