3Bellringer #7A 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 BForces always act in pairs:a. Trueb. False
4BELLRINGERREAD THE FIRST PARAGRAPH ON PAGE 11 OF YOUR BOOK. THINK ABOUT OTHER WAYS YOU HAVE HEARD THE WORD FORCE USED.
5THERE 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 MOTIONWITHOUT A FORCE THERE WOULD BE NO MOTION
6FORCES ALWAYS OCCUR IN PAIRS Force gives an object the energy to move, stop moving, or change direction.
7Examples 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.
8HOW DOES FORCE CAUSE MOTION? Motion is a result of UNBALANCED FORCES.UNBALANCED FORCE is the total force on an object in one direction .
9REMEMBER: 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.
10EXAMPLES OF UNBALANCED FORCES PUSHING A SHOPPING CARTSKIING DOWNHILL
11WHAT IS A BALANCED FORCE? Balanced Forces cause no motion. The paired forces occur in opposite directions and are of equal force.
12EXAMPLES OF BALANCE FORCE Two dogs of equal strength playing tug of warSkier on a flat surface
16Friction - The force that opposes motion between two surfaces. FRICTION : FORCE THAT OPPOSES MOTIONFriction - 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.
17All of these questions deal with friction !!!!! Would you rather catch a ball diving in the grassor 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 yourhands?All of these questions deal with friction !!!!!
18FACTORS THAT AFFECT THE AMOUNT OF FRICTION 1. Roughness - The more rough the surface; morefriction created.2. Force - The more force pushing the object; themore friction between valleys.3. Attraction between objects(static) - The greaterthe attraction; the more friction created.
19Humans 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?
20The 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.
21TYPES OF FRICTION1. Sliding Friction2. Rolling Friction3. Fluid Friction
22SLIDING FRICTIONDefinition - Friction caused by objects sliding across one another.Examples - Pushing an object (dresser), sledding, brakes, chalk
23ROLLING FRICTIONDefinition - 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,
24FLUID 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?
25STATIC FRICTIONDefinition - 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.
26WAY 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.
27WAYS FRICTION CAN BE HARMFUL 1. Friction in the engine causestemperature to rise.2. Wind and water causes erosion.3. Holes in you jeans.4. Hard to move heavy objects.
28WAYS TO REDUCE FRICTION 1. Lubricant(liquid or gas)2. Wheels3. Ball bearings4. Make surfaces that rub against eachother smoother.
29WAYS TO INCREASE FRICTION 1. Make surface rougher(sand on iceor batters glove).2. Increase the force pushing thesurfaces together.
30Name the different types of friction. Give examples of each.
33Gravity, Free Fall, and Air Resistance Gravity - the force that pulls objects towardone another.Free Fall – when only gravity is acting on anobject. This is rare because of air resistance.All objects free fall at a rate of 9.8 m/s. Agolf ball and basketball will hit the groundat the same time.Air Resistance – type of fluid friction whichincreases with the surface area of the object.