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Ch 3 8th Gd Sci 2013
Chapter 3 - Forces, Momentum, and Associated Laws
| Question | Answer |
|---|---|
| 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
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