8th Grade - Chapter 2, Section 2 ~ Friction and Gravity
What types of friction are easiest to overcome?
Fluid friction and rolling friction
What types of friction occur when you ride your bike through a puddle?
Fluid friction and rolling friction
How does the direction of friction compare to the direction of motion?
Friction acts in the opposite direction of motion
What is static friction?
Friction that acts on objects that are not moving
What is fluid friction?
Friction that occurs when a solid object moves through a fluid
What is rolling friction?
Friction that occurs when an object rolls over another
What is sliding friction?
Friction that occurs when one solid surface slides across another
An astronaut can easily jump on the moon. How do his mass and weight compare to his mass and weight on the Earth?
His mass is the same on both surfaces, but his weight is a lot smaller on the moon.
Why is it more difficult to walk on ice than pavement?
Ice is smoother than pavement.
How does distance affect the gravitational attraction between objects?
The farther apart the objects are, the weaker the attraction is
When is terminal velocity reached?
The force of air resistance equals the object's weight
Why do objects in free fall accelerate as they fall?
The force of gravity is an unbalanced force. Objects closer to the Earth expierience more gravity.
How does gravity affect objects that are moving horizontally?
The force of gravity is the same
What is weight?
The force of gravity on a person or object on a planet.
What is friction?
The force that two surfaces rub on each other when they rub together
Why don't you notice the pull of gravity between most objects?
The gravitational force is too insignificant
What is terminal velocity?
The greatest velocity a falling object reaches
What is mass?
The measure of the amount of matter in an object
The sun's mass is about 300,000 times bigger than the Earth's mass, yet our moon orbits around the Earth, not the sun. Why?
The moon is a lot closer to the Earth than the sun.
How does mass affect the gravitational attraction between objects?
The smaller the mass, the smaller the gravitational force. Same holds true for all other sizes.
What two factors affect the force of friction?
The surfaces involved and how hard the objects are pushing together
What instrument do you use to measure mass?
Triple beam balance
Air resistance increases with:
Velocity
What are examples of rolling friction?
Wheels on a vehicle or a ball rolling down a hill
What is free fall?
When the only force acting on an object is gravity
What are examples of static friction?
When you push against a heavy object, such as a car
Do all objects fall at exactly the same rate, with out air resistance?
Yes
Will a free falling object stop accelerating?
Yes, because of terminal velocity
What is the acceleration rate due to gravity on Earth?
9.8 m/s squared
Two identical balls are thrown. One ball is horizontally thrown and the other is dropped vertically. Does the horizontal velocity affect how fast it falls?
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Why do slippery fluids such as oil reduce sliding friction?
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What is air resistance?
A fluid friction - the upward force exerted on falling objects
What is gravity?
A force that pulls objects together
Does a smooth surface or rough surface produce more friction?
A rough surface
What instrument do you use to measure weight?
A scale
Besides gravity, what other force acts on falling objects?
Air resistance
What force changes when a sky diver's parachute opens? What force stays the same?
Air resistance and gravity
What is a projectile?
An object that is thrown
What are examples of sliding friction?
Slipping on ice or using a hand brake on a bicycle
What are the four types of friction?
Static Sliding Rolling Fluid
What type of friction requires the greatest force to get an object moving?
Static friction
What kind of friction allows you to walk without slipping?
Static friction and sliding friction
What factor has an effect on air resistance?
Surface area. Greater surface area = greater air resistance
What are examples of fluid friction?
Swimming and skydiving
How does the mass of an object affect its acceleration during free fall?
It doesn't
What is Newton's Law of Gravitational Force?
It states that the force of gravity acts between all objects in the universe
What two factors affect the gravitational attraction between objects?
Mass and distance
Everything that has mass is made up of:
Matter
Without friction, when might a moving object stop?
Never, unless another force acted on it.
What would happen you your weight on the surface of a planet much bigger than Earth? Why?
Your weight would be greater because the planet's mass is so much bigger. The gravitational force is much bigger.
What is the SI unit for mass?
kg (kilogram)
