Friction and Gravity,

IQ pg 64 What is friction? Describe everything you think you know.

Friction pg 65 A force that opposes (goes against) motion Occurs when two surfaces exert force on each other when they rub against each other. Caused when irregularities of one surface come into contact with those of another surface, Strength of the force of friction depends on: types of surfaces involved and how hard the surfaces push together.

Rough surfaces: more friction Ex. Rocks, sand, road, tectonic plates, concrete, sandpaper, carpet, tree bark, heavily treaded tire Smooth surfaces: less friction Ex. Lab table, ice, oil, marble, water, polished surfaces, tiles, whiteboard

Types of Friction 1. Static (not moving) Friction: Is a friction that acts on objects that are not moving. 2. Sliding Friction: Occurs when two solid surfaces slide over each other. 3. Rolling Friction: Occurs When an object rolls over a surface. 4. Fluid Friction: Occurs when a solid object moves through a fluid. (fluids in science are all the liquids and gases)

WHAT TYPES OF FRICTION?

In Partners: p123 as a guide List as many ways that you can think of how friction is: HARMFUL IN DAILY LIFE (in situations, harmful to objects…when do you not want it?) HELPFUL IN DAILY LIFE (situations, when do you need friction?)

WARM UP: Get ready to go over homework from last night FRICTION LAB continued today

Which surface has the most friction and least friction? Using a hot wheel car, you will test various surface types: Lab table Cloth towel/blanket sandpaper

Make a hypotheses on which surface will have most friction and why Make a short ramp out of a piece of cardboard and one or two books on a table. 2. Put a toy car at the top of the ramp and let go. If necessary, adjust the ramp height so that your car does not roll off the table. 3. Put the car at the top of the ramp again and let go. Record the distance the car travels after leaving the ramp. Do this three times, and calculate the average for your results. 4. Change the surface of the table by covering it with sandpaper or cloth. Repeat step 3. Change the surface one more time, and repeat step 3 again.

Create a Data Table for Results pg 67 Trial 1 Length in cm Trial 2 Trial 3 AVERAGE OF ALL 3 TRIALS Table alone   Sandpaper Towels

Analysis questions Which surface had the most friction? Why? What do you predict would happen if the car were heavier? What do you predict would happen if the car were lighter? Record your results and answers in your notebook on page 67.

IQ 12/5/13 pg 68 Gravity is a type of force: Explain what you know about gravity and how it works

Gravity Pg 69 Gravity is a force that pulls objects toward each other.

Gravity depends on Mass and Distance; The force of gravity between objects: increases with greater mass decreases with greater distance.

Universal Gravitation Law of Universal Gravitation states that the force of gravity acts between all objects in the universe. Because the Earth is by far, the largest and closest object around, it has the greatest force of attraction...

Weight=Mass X Acceleration due to gravity Mass: amount of matter in an object SI unit of mass is gram (g) or kilogram (Kg). Weight is a measure of gravitational pull. Weight=Mass X Acceleration due to gravity Acceleration due to gravity is 9.8m/s/s

What happens to gravity when you move farther away?

Mass and Weight are two different Properties of Matter Mass is a physical property of matter that explains how much matter is in an object Mass does not change when gravity changes WEIGHT Weight is a force which is calculated by multiplying the acceleration of gravity times mass. Weight can change when gravity changes

Gravity and Motion Free fall: An object is in free fall when the only force acting on the object is gravity. In Free Fall, the force of gravity alone causes an object to accelerate in the downward direction. The acceleration due to gravity is 9.8m/s/s.

Air Resistance is an upward force exerted on falling objects. Air Resistance is a type of fluid friction acting on all falling objects. Objects with greater surface area experience more air resistance as they fall.

When objects are thrown horizontally they travel in a projectile motion.