# Science - Gravity and Friction

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### gravity

the force that attracts two masses to each other

### strength of gravity depends on two things

mass and distance

### What happens to frictional force as you continue to push an object?

It remains constant but at a lesser level once the object is moving.

### friction

resistance due to the motion of two objects in contact

### ways to increase friction

increase the weight of the object, rough surface, move surfaces against each other, etc.

### ways to decrease friction

wheels, decrease the weight of the object, smooth surface, resist movement between surfaces, etc.

### Air resistance

the friction due to air; affected by speed and surface area

### Mass

the amount of matter in an object; does not change depending upon location

### Weight

the measure of the downward pull of gravity; changes depending upon where you are in the universe

### Terminal Velocity

the point at which an object can no longer accelerate; air resistance meets gravity

### How do objects orbit?

The balance between the mass of two objects and the distance of the two objects are perfect.

### What three things does friction depend upon?

types of surfaces, motion of surfaces, how hard the surfaces are pushing together

### How does friction produce heat?

molecules on the surface move faster and the temperature increases

### Four types of friction

rolling, sliding, static, fluid

### static

not moving or changing

liquid or air

### rolling

wheels or ball-bearings

### sliding

what we tend to think of when we say friction; objects rub together

### If I drop a math book and a novel at the same time, which will be most affected by air resistance?

The math book, because its surface area is bigger. Gravity will act the same on both of them but air resistance will want to push the math book up with more force.

### How does your weight and mass on Earth compare with your weight and mass on Jupiter? Why?

Because Jupiter has so much more mass than Earth, it has much stronger gravity, so I would weigh a lot more. My mass is the same, because the amount of matter in me hasn't changed.

### How does gravity, terminal velocity, and air resistance work on a penny when it is dropped from a 50 story building?

Gravity pulls the penny down, but air resistance pushes the penny up against gravity. At a certain point, air is pushing up on gravity so much that gravity can't accelerate anymore. This is when the penny reaches terminal velocity.

### If I throw something forward and drop something at the same time, when do each of the objects land?

At the same time. Gravity pulls everything at the same rate.

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