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# Ch 3 8th Gd Sci 2013

### Chapter 3 - Forces, Momentum, and Associated Laws

QuestionAnswer
Any push or pull on an object Force
The net force exerted on an object will produce a proportional acceleration. That is, if a force acts on something, it accelerates. Newton’s 2nd Law of Motion.
What explains the relationships among mass, force and acceleration? Newton’s 2nd Law of Motion – F(force) = m (mass) • a (acceleration)
The force that opposes motion between two surfaces in contact with (sometimes rubbing against) each other Friction
Type of friction between 2 surfaces that are not moving past each other Static Friction – Static means stationary, not moving
Type of friction between 2 surfaces that are sliding past each other Sliding Friction – example: When a car skids, its locked wheels slide over the road surface.
Type of friction between the wheels of a car in motion and the road Rolling Friction – In this example, the wheels of the car are moving, or rolling.
The force exerted by air on a moving object Air resistance
The largest velocity reached by a falling object when the force of air resistance equals the force of gravity Terminal velocity
The force every object in the universe exerts on every other object Gravity
This law states that the size of the gravitational force between 2 objects depends on their masses and the distance between them Law of Universal Gravitation
The pull of gravity on an object Weight
The amount of matter in an object Mass
When gravity is the only force acting on a falling object (there is no air resistance) Free Fall
The force that keeps an object moving in a circle Centripetal Force
The type of acceleration a space shuttle in orbit has due to gravity and inertia Centripetal Acceleration
Anything thrown or shot through the air Projectile
The path of a projectile Trajectory
What type of path does a projectile have on Earth, and why? A curved path, because gravity pulls it toward the center of the Earth.
What law can be stated as “to every action, there is an equal and opposite reaction”? Newton’s 3rd Law of motion
The property of a moving object resulting from its mass and velocity Momentum (p= m • v)
In the formula p= m • v, what does the p stand for? Momentum
In the absence of external forces, total momentum in a system is conserved Law of Conservation of Momentum
What might the Law of Conservation of Momentum help us do? Predict the motion (speed and direction) of objects in a collision
The weld bond or sticking that occurs where bumps of 2 surfaces touch each other, causing friction microweld
What must you apply to break the microwelds that create friction? Apply enough Force to overcome them.
What force keeps moons in orbit around the planets? Gravity
In the absence of air, how would objects dropped from the same height fall? At the same rate
If objects of different masses are dropped from the same height (no air resistance), which will hit the ground first? They will hit at the same time.
If a ball and a feather are dropped through the air at the same time, what causes the feather to fall more slowly? air resistance
If a brick is dropped from a height at the same time that another brick is thrown horizontally from the same height, which will hit the ground first? They will fall at the same rate, and reach the ground at the same time, because gravity will accelerate them to the ground at the same rate.
What is the size of the force of gravity on earth? 9.8 m/s2 towards the center of the earth
As the distance between 2 objects increases, what decreases? The gravitational pull between the 2 objects
A good marksman knows that projectile motion means you must aim where to hit the bullseye? Above the bullseye
How do we measure Mass in Science? We measure mass in kg, using a balance.
How do we measure Weight in Science? We measure weight in Newtons, using a spring scale.
What accelerating force creates the difference between Mass and Weight? Gravity (9.8 m/s2 toward the center of the Earth)
Because of the Law of Universal Gravitation, as you climb up a mountain, or ascend in a plane, your weight will _____ decrease
What law is used to explain the motion of objects after a collision? Conservation of Momentum
What would cause the momentum of a massive object to be 0 N? If the object was not moving, its velocity would be 0 m/s2. Since p= m • v, any mass with a velocity of 0 m/s2 would have a momentum of 0 N.
Use Newtons third law to explain how a rocket moves. The rocket pushes hot gases backwards and the hot gases push the rocket forward.
Use Newton's third law of motion to explain how a person runs. A person's foot pushes the ground backwards and down, and the ground pushes the foot, and the attached person, forwards and up.
Created by: judi829