Module 2: Forces, Energy and Motion

Question 1

Define Potential Energy

Answer 1

the energy a system has due to it’s shape and position; can be thought of as the potential work to do

Question 2

Give an example of Potential Energy

Answer 2

an exercise band (energy is zero when not used, but energy increased when in use)

Question 3

Give an example of Electrical Potential Energy

Answer 3

energy between clouds and the ground in a thunderstorm

Question 4

Give an example of Chemical Potential Energy

Answer 4

food and gasoline (energy stored in molecular bonds)

Question 5

Give an example of Gravitational Potential Energy

Answer 5

water being pumped to the top of a water tower

Question 6

Explain how a change in mass of an object can affect the gravitational potential energy of that object. Explain how a change in height can affect it.

Answer 6

increasing mass or acceleration due to gravity or height will also increase gravitational potential energy; same can be said for decreasing, a decrease in one side of the equation will decrease the other side

Example:

• if a helicopter goes higher in altitude, the gravitational potential energy increases
• if the helicopter hoovers using more fuel, this decreases the mass of the helicopter and decreasing the gravitational potential energy

Question 7

What is the equation for Gravitational Potential Energy?

Answer 7

Mass x Acceleration due to Gravity x Height

Question 8

Define Kinetic Energy and give examples.

Answer 8

Definition: simply the energy an object has due to its motion

Example: a moving vehicle, a flowing river, a rolling or spinning ball, a person running, wind, skydiver falling, a thrown baseball

Question 9

Explain what happens to kinetic energy when the mass and speed of an object changes.

Answer 9

• If an object is maintaining a certain speed, but losing mass in the process then it is losing kinetic energy.
• If an object slows its speed then it decreases its kinetic energy
• If an object speeds up thenits kinetic energy increases

Question 10

Define Thermal Energy and give an example

Answer 10

Definition: another form of kinetic energy; the molecules within a material have kinetic energy and the faster they move, the more thermal energy the molecule has

Example: heat a cup of coffee, fire, your home’s furnace

Question 11

Explain the Law of Conservation of Energy

Answer 11

• energy cannot be created or destroyed it can only change form
• even though the type of energy can change (potential to kinetic) the toal amount of energy remains constant

Question 12

Define Gravitational Force

Answer 12

• the force between two objects that have mass; or any two objects that mass will exert a gravitational force
• the more massive the objects, the greater the gravitational force between them
• the further the objects are away from each other, the smaller the gravitational force between them

Question 13

Define Projectile Motion and give an example of an object that exhibits projectile motion, and describe the forces that are acting on it

Answer 13

Definition: a form of motion in which an object or particle (in either case referred to as a particle) is thrown near the Earth’s surface and it moves along a curved path under the action of gravity only

Examples:

• a cannonball fired from a cannon
• a baseball being thrown across a field
• a baseball hit in the air by a bat
• a person jumping on a trampoline

FYI - a frsbee would not be an example because the shape and the rotation in the air helps to keep it in the air

Question 14

Explain how an object becomes a satellite

Answer 14

Definition: essentially a body in freefall that has a sideways motion fast enough that the parabola it forms literally encircles the Earth

• if the object’s speed is too slow, the object will spiral inward until it finally impacts the Earth
• if the object’s speed is too fast, the object will escape the Earth’s gravitational pull

Question 15

Explain the role of gravity in the formation of solar systems and galaxies. Explain how gravity creates spinning disks of material that form solar systems and galaxies.

Answer 15

Solar systems and galaxies can start out as clouds of gas and dust (Nebulas). These clouds have mass and are affected by gravity. This can cause them to collapse in on themselves and the particles inside to spin in the same direction. At some point the Nebula center becomes massive enough that a protostar is formed, enventually becoming a full-blown star. These stars have discs of material forming that have enough velocity to sucks chunks of matter into the disc to orbit the star.

Question 16

Describe the movement of objects in our solar system.

Answer 16

Our planets travel around our sun in mostly circular manner, like they are on discs. Though the planets furtherest from the sun thend to travel more elliptically. Though we do have comets that can come from far out of the solar system, pass close to the sun and return to the far reaches of the solar system.

Question 17

Explain why the same side of the Moon always faces the Earth.

Answer 17

The moon rotates at a speed such that is rotation keeps the same side of the moon facing the Earth throughout its orbit; or the Earth ahs caused the moon to rotate on its axis at just the right speed that the same side of the moon always faces the Earth

Question 18

Describe the role gravity plays in the formation of stars. Describe the role it plays throughout the life of a star. Discuss the relationship between thermal energy and gravitational force in a star.

Answer 18

Low-mass stars can live many billions of years because of their low rates of fusion. Stars with enough mass can fuse certain elements causing them to consume more energy that it releases. Gravity will pull the outer layer of the star inward causing it to explode into a supernova.

Question 19

Explain how a gravitational field affects light

Answer 19

If light travels in a straight line through space, and space itself is warped by gravity, then light will appear to follow a curved path from an outside observer.

Question 20

Describe how light will behave in a black hole and why.

Answer 20

A black hole is so massive that it traps light. If light travels in a straight path it has nowhere to go and there is no way to pull it out of the black hole.

Question 21

True or False

Newton predicted that gravity is a force that acts between objects with mass. Einstein predicted that gravity can bend space allowing it to act on light.

Answer 21

True

Increasing the mass of objects increase the gravitational force between the two objects

Question 22

Define Direct Relationship

Answer 22

this is where two variables do the same thing; that is, if one increases so does the other and vice versa

Question 23

Describe how Gravitational Force and Mass are examples of Direct Relationships

Answer 23

Gravitational Force and Mass: if you increase the mass of two objects, this increases the gravitational force between the two (and vice versa)

Question 24

Describe how Electrical Force and Charge are examples of Direct Relationships.

Answer 24

Electrical Force and Charge: opposites attract and likes repel

Question 25

Describe Inverse Relationships

Answer 25

this is where two variables do the opposite; if one variable increases, then the other variable decreases

Question 26

Describe how Gravitational Force and Distance are examples of Inverse Relationships.

Answer 26

Gravitational Force and Distance:

decreasing the distance between two objects of equal mass will increase the gravitational force

Question 27

Describe how Electrical Force and Distance are examples of Inverse Relationships.

Answer 27

Electrical Force and Distance:

the electrical force is strongest between two objects of equal mass are closest to one another

Question 28

Describe Newton’s Law of Universal Gravitation.

• Identify the factors that contribute to the strength of graviational force.
• Explain how those factors affect the strength of the force.

Answer 28

• Newton’s Law of Universal Gravitation simply states that between any two objects with mass there exists a gravitational force between them
• the mass of objects, distance between objects

Question 29

Describe Coulomb’s Law of Electrical Force.

• Identify the factors that contribute to the strenght of electrical force.
• Explain how those factors affect the strength of the force.

Answer 29

• Coulomb’s Law explains the force between two electrostatic charges
• opposites attract, and likes repel

Question 30

Identify electrical force and gravitational force as vector or scalar.

Answer 30

• Vector - quantities that have measure of both a magnitude and direction (Electrical Force)
• Scalar - quantities tha don’t have a direction, only magnitude (Gravitational Force)
• VectorScalar

velocity speed

force pressure

acceleration mass

momentum energy

temperature

Question 31

Explain what affects the direction of electrical force.

Answer 31

The direction of the electrical force is dependent upon whether the charged objects have like charges or opposite charges.

Question 32

Define Magnetic Force. Explain what makes an object magnetic.

Answer 32

Definition: attraction or repulsion that arises between electrically charged particles because of their motion

• magnetism only acts on charged particles and the charge must be moving and not moving parallel to the magnetic field; magnetic fields facing the same direction

Question 33

Describe a Magnetic Field.

Answer 33

areas where an object exhibits a magnetic influence; generated when electric charge carriers such as electrons move through space or within an elecrical conductor

Question 34

Differentiate magnetic force from electrcal force.

Answer 34

Electrical Force: doesn’t care about motion, it only cares about charge

Magnetic Forces: only act on charged particles; requires the charges to be moving; can both attract and repel objects

Question 35

Explain what happens to charged particles in a magnetic field.

Answer 35

A charged particle placed in a magnetic field executes a circular orbit in the plane perpendicular to the direction of the field

Question 36

Which characteristics apply to the statement below, Electricity, Magnet or both:

Is a flow of charges measured by current?

Answer 36

Electricity

Question 37

Which characteristics apply to the statement below, Electricity, Magnet or both:

• Always has a north and south pole

Answer 37

Magnet

Question 38

Which characteristics apply to the statement below, Electricity, Magnet or both:

• Resistance measure in ohms

Answer 38

Electricity

Question 39

Which characteristics apply to the statement below, Electricity, Magnet or both:

• Indicated with a compass

Answer 39

Magnet

Question 40

Which characteristics apply to the statement below, Electricity, Magnet or both:

• Opposites attract

Answer 40

Magnet

Question 41

Which characteristics apply to the statement below, Electricity, Magnet or both:

• Produced by charged particles that are spinning in the same direction bt are not flowing from on atom to another

Answer 41

Both Electricity and Magnet

Question 42

Define Newton’s First Law of Motion and give an example.

Answer 42

Definition:

• every object continues in its state of rest, or a uniform speed in a straight line, unless acted on by a nonzero force
• an object at rest tends to stay at rest and an object in motion tends to stay in motion, unless acted on by a net force

Examples:

• when driving a car and you slam on the breaks, your body still continues to move forward (objects in motion)
• party trick - pulling the tablecloth so quickly all items on the table stay there and don’t move (objects at rest)
• Objects are lazy and don’t want to change what they are doing

Question 43

Define Newton’s Second Law of Motion and give examples.

Answer 43

Definition: F = ma

• the acceleration produced by a net force on an object is directly proportional to the net force, is in the same direction as the net force and is inversely proportional to themass of the objects
• if acted upon by a net force, an object will accelerate (as mass increases, acceleration decreases)

Examples:

• an elephant on roller skates vs a mouse on roller skates
• a hand pushing a brick

Question 44

Define Newton’s Third Law of Motion and give an example.

Answer 44

Definition:

• whenever on object exerts a force on a second object, the second object exerts anequal and oposite force on the first
• for every action there is an equal and opposite reaction; you cannot touch without being touched

Examples:

• leaning against a wall with your and hand
• hammer hitting a nail
• insect hitting a windshield, insect gets squished but the windshield just gets dirty

Question 45

Describe what the equation F=ma means and how it relates to Newton’s Second Law of Motion.

Answer 45

F = ma

Force = mass x acceleration

• if mass increases, acceleration decreases
• Second Law is inversely proportionate

Question 46

A child is pulling a wagon around the yard. As she goes, the child picks up toys and places them in the wagon until its full. If she continues to pull the wagon with the same amount of force that she used when she first began, what will hapen to her acceleration?

1. it will decrease
2. it will increase
3. it will stay the same

Answer 46

1. it will decrease

• it will decrease because as mass incresases, acceleration decreases
• this example describes Newton’s Second Law of Motion

Question 47

A golf ball hits the side of a tree. What experiences more force, the golf ball or the tree?

1. the tree
2. the golf ball
3. each experience the same amount of force

Answer 47

3. each experience the same amount of force

• though the golf ball is more affected by the interaction because it has less mass than the tree
• this is an example of Newton’s Third Law of Motion

Question 48

You board a bus to travel across town. The bus suddenly starts, causing you and the rest of the passengers to lurch backwards. This is an example of:

1. Newton’s First Law of Motion
2. Newton’s Second Law of Motion
3. Newton’s Third Law of Motion
4. Inertia in action
5. F=ma in action

Answer 48

4. Inertia in action