Chapter 4 - Motion & Gravity

Question 1

Acceleration

Answer 1

The rate at which velocity is changing

Question 2

Energy

Answer 2

The ability to do work

Question 3

Force

Answer 3

A push or pull exerted on an object

Question 4

Free fall

Answer 4

A state in which the only force acting on an object is gravity

Question 5

Momentum

Answer 5

The product of mass and velocity

Question 6

Speed

Answer 6

How fast something is travelling

Question 7

Velocity

Answer 7

How fast something is travelling, and in which direction

Question 8

Weightless

Answer 8

In a state of free fall

Question 9

Isaac Newton

Answer 9

Developed laws of motion and gravity that can be applied to planetary motion in our Solar System

Question 10

Johannes Kepler

Answer 10

Developed laws of planetary motion using observations made by Tycho Brahe

Question 11

Can an object have a constant speed but a changing velocity?

Answer 11

Yes; because if direction is changing, then so is velocity, even if speed is constant

Question 12

Can an object have a changing speed and a constant velocity?

Answer 12

No; because if speed is changing velocity must also be changing

Question 13

How are velocity and acceleration related?

Answer 13

Acceleration is the rate of change of velocity. They can have the same signs, same direction, or different signs/directions.

Question 14

What is Newton’s First Law of Motion?

Answer 14

An object at rest will remain at rest, and an object in motion will remain in motion, unless acted upon by a net force

Question 15

What is Newton’s Second Law of Motion?

Answer 15

A force contributes to a change in velocity

Question 16

What is Newton’s Third Law of Motion?

Answer 16

For every action, there is an equal and opposite reaction

Question 17

If the same force is applied to two objects, which has the largest acceleration?

Answer 17

Whichever has the smaller mass, as force = mass x acceleration

Question 18

When you sit in a chair, how is the force you exert on the chair related to the force the chair exerts on you?

Answer 18

You exert a downward force on the chair. The chair exerts an equal upward force on you.

Question 19

Describe the law of conservation of energy.

Answer 19

In an isolated system, energy remains constant

energy cannot be created or destroyed, it can only change forms

Question 20

Describe the law of conservation of momentum.

Answer 20

In an isolated system, the total momentum of all objects in the system remains constant

momentum cannot be created or destroyed, but can be transferred between objects

Question 21

Describe the law of conservation of angular momentum.

Answer 21

In an isolated system, the angular momentum of an object remains constant unless acted upon by an external force

Question 22

Kinetic energy

Answer 22

The energy of motion

Question 23

Potential energy

Answer 23

Energy that is stored ; depends on the relative locations of different parts of a system

Question 24

Radiative energy

Answer 24

Energy carried by light (electromagnetic radiation)

Question 25

Describe Newton's Law of Gravitation.

Answer 25

For two objects located a distance apart, the force of gravity is proportional to the product of their masses divided by the distance squared

Question 26

How did Newton's laws extend Kepler's laws?

Answer 26

Newton's laws explained the observations described in Kepler's laws ; specifically, that the force causing these observations is gravity

Question 27

What is Newton's form of Kepler's third law?

Answer 27

The square of a planet's orbital period around a star is directly proportional to the cube of its semimajor axis, with the constant of proportionality depending on the combined masses of the star and planet

Question 28

A planet orbits a star. What will happen to the orbital period of the planet if the mass of the star increases or decreases?

Answer 28

Mass increases - the orbital period will decrease Mass decreases - the orbital period will increase ## Footnote Why? Stronger gravity means a faster orbital speed, and vice versa

Question 29

What types of orbits are bound?

Answer 29

Circular and elliptical

Question 30

What types of orbits are unbound?

Answer 30

Parabolic and hyperbolic

Question 31

If the radius of a planet increases while its mass stays the same, what happens to its surface gravity?

Answer 31

Surface gravity will decrease ## Footnote Increased r = greater distance from center of mass, which means weaker gravity

Question 32

If the mass of a planet increases while its radius remains the same, what happens to its surface gravity?

Answer 32

Surface gravity increases ## Footnote Increased mass with same r = stronger gravity

Question 33

If Earth's mass increased but its radius stayed the same, what would happen to your weight?

Answer 33

Your weight would increase ## Footnote because Earth's gravity pulling on you would also increase

Question 34

If Earth's radius increased but its mass stayed the same, what would happen to your weight?

Answer 34

Your weight would decrease ## Footnote because Earth's gravity pulling on you would decrease