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(Forces and Energy Part 1a : Forces and Energy)
What is potential energy?

- the energy a system has due to its shape, position
- potential energy can be thought of as the potential to do work
- example : exercise band, the potential energy is increased as the person stretches the band
- electrical potential energy : thunderstorm, lightning touches the ground
- chemical potential energy : energy stored in molecular bonds, food, gasoline
- gravitational potential energy : water being pumped to the top of a water tower

1

(Forces and Energy Part 1a : Forces and Energy)
Give some examples of different types of :
(A) potential energy
(B) electrical potential energy
(C) chemical potential energy
(D) gravitational potential energy

(A) potential energy :
- archer's bow string pulled back, coiled spring, unopened carbonated drink, child at the top of a slide
(B) electrical potential energy : television before it is turned on, light bulb that is turned off, car headlights before they are turned on, solar cells at night
(C) chemical potential energy :
- charged battery, wick in a candle, gasoline before it's ignited, fireworks before they are launched
(D) gravitational potential energy :
= mass x acceleration due to gravity x height
- depends on the mass, acceleration due to gravity and height of an object
- stone hanging off the edge of a cliff, me sitting in a chair, any times there is an object above ground has gravitational potential energy

2

(Forces and Energy Part 1a : Forces and Energy)
How does a change in mass of an object affect the gravitational potential energy of that object? How does a change in height affect it?

- the greater the distance from earth's center, the less the gravitational force on an object
- no matter how great the distance, gravity approaches, but never quite reaches zero
- there is still gravitational attraction between any two masses, no matter how far apart they are
- gravity gets weaker with distance, the same way a light gets dimmer as you move farther from it

3

(Forces and Energy Part 1a : Forces and Energy)
What is kinetic energy? List examples of objects with kinetic energy.

- kinetic energy is simply the energy an object has due to its motion
- anything that is moving has kinetic energy : a moving vehicle, a flowing river, a rolling or spinning ball, a person running, wind, a skydiver falling, a baseball thrown across the field

4

(Forces and Energy Part 1a : Forces and Energy)
Explain what happens when the mass and speed of an object changes.

- when two objects have the same mass but one object has a greater speed, the object with the greater speed has more kinetic energy
- when two objects have equal speed, the object with the greater mass has more kinetic energy
- kinetic energy = (1/2) x Mass x Velocity(squared)

5

(Forces and Energy Part 1a : Forces and Energy)
Define thermal energy

- thermal energy is just another form of kinetic energy
- in the case of thermal energy, the molecules within a material have kinetic energy
- the faster they move, the more thermal energy the molecule has
- examples : heat of a cup of coffee, fire, your home's furnace
- low movement, low temperature; high movement, high temperature

6

(Forces and Energy Part 1a : Forces and Energy)
Explain the law of conservation of energy.

- states that energy cannot be created or destroyed it can only change form
- does not apply to nuclear reactions and at quantum (extremely small and short duration) scale
- when an object burns, it's chemical energy is being released as thermal energy or infrared radiation
- states that the total energy released as thermal energy and electromagnetic radiation is equal to the chemical potential energy lost by the burning material
- roller coaster : maximum potential energy is at the top of the hill, as the rollercoaster moves down the track, potential energy is converted to kinetic energy, the total energy of the rollercoaster remains constant

7

(Forces and Energy Part 1a : Forces and Energy)
What is gravitational force?

- force between two objects that have mass, in other words, any two objects that have 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

8

(Forces and Energy Part 1b : Gravity)
What is projectile motion? Give an example of an object that exhibits projectile motion, and describe the forces that are acting on it.

- an object that is projected vertically by some means and continues in motion with it's own inertia while gravity acts on the object at the same time will eventually bring it down to the ground.
- vertical velocity decreases as the projectile gets closer to its peak height (kinetic energy is converted to potential energy)
- horizontal velocity does not change
- example : water coming out of a water fountain; it shoots up and curved back downs cannon ball fired from a cannon, baseball thrown or hit with a bat, a person jumping on a trampoline, a rock fired from a catapult
- examples that are NOT projectile motion : rocket, airplane, bird, frisbee

9

(Forces and Energy Part 1b : Gravity)
How does an object become a satellite?

- is defined as an object in a stable orbit around a larger astronomical body
- if an object has enough speed, it can escape the earth's gravitational field rather than enter an orbit or falling back to the earth's surface
- this velocity is known as escape velocity
- the object moves sideways, gravity pulls the object towards the center of the larger object, the object follows an elliptical path as it falls around the larger body

10

(Forces and Energy Part 1b : Gravity)
Explain the role of gravity in the formation of solar systems and galaxies. How does gravity create spinning disks of material that form the solar systems and galaxies?

- gravity (clouds of dust and materials) within a nebula causes it to slowly collapse
- eventually the nebula collapses enough to form a star, as the nebula collapses, it's angular momentum causes a spinning disk to form
- eventually gravity causes larger chunks in the disk to for; these larger chunks attract more and more material and eventually can form planets; as the protostar grows and continues to collapse due to gravity, eventually it will become massive enough for nuclear fusion to ignite
- disks are formed of materials bound to an object by gravity
- orbits of planets, tidal locking, the sun and stars, classification of planets, dwarves, and other objects; orbits of comets, asteroids and moons; presence of the asteroid belt; geological activity on moons of gas giants; subsurface oceans on moons of gas giants

11

(Forces and Energy Part 1b : Gravity)
Describe the movement of objects in our solar system.

- objects in the inner solar system tend to orbit on a plane
- most of the planets and larger moons rotate in the same direction
- comets and objects further out tend to orbit at an incline relative to the inner solar system

12

(Forces and Energy Part 1b : Gravity)
Why does the same side of the Moon always face the Earth?

- the moon rotates at a speed such that it's rotation keeps the same side of the moon facing the earth throughout its orbit (synchronous rotation)
- also explains the rotation of other objects in the solar system : Pluto/Cheron, some moons of Neptune, Uranus, Saturn, Jupiter, and both moons of Mars, possibly Mercury around the sun, also seen in nearby stars

13

(Forces and Energy Part 1b : Gravity)
What role does gravity play in the formation of stars? What role does it play throughout the life of a star?

- nebula collapses into stars
- fusion occurs
- evolves into low mass stars, sun like stars, and/or large mass star

14

(Forces and Energy Part 1b : Gravity)
What is the relationship between thermal energy and gravitational force in a star?

- thermal energy : exerts a force from the center of a star outwards
- gravitational force : exerts a force on the outside of a star pushing inwards toward the center
- when these two forces balance out, the star has reached its size and mass

15

(Forces and Energy Part 1b : Gravity)
How does a gravitational field affect light?

- I'm 1915 Albert Einstein published his paper on general relativity :
- gravity has the ability to bend space
- a photon traveling in a straight line from its perspective will travel in a curved path in the presence of a gravitational field

16

(Forces and Energy Part 1b : Gravity)
How will light behave in a black hole? Why?

- a black hole is the remains of a super giant star that has collapsed on itself
- if an object is large enough it can bend space to the point of a singularity
- if this is the case, then a photon can be trapped in that singularity

17

(Forces and Energy Part 2a : Coulomb's Law and Newton's Law of Universal Gravitation)
Define Newton's Law of Universal Gravitation. What factors contribute to the strength of a gravitational force?

- every mass pulls on every other mass with a force that is directly proportional to the product of the two interacting masses
- the force is inversely proportional to the square of the distance separating them

18

(Forces and Energy Part 2a : Coulomb's Law and Newton's Law of Universal Gravitation)
Explain what happens to the gravitational force when there is a change in mass and/or distance.

- the greater the mass, the grater the force of gravity exerts, so the more attracted to each other they will be
- when objects are pulled further apart, the force of gravity becomes weaker

19

(Forces and Energy Part 2a : Coulomb's Law and Newton's Law of Universal Gravitation)
Define Coulomb's Law of electrical force. What factors contribute to the strength of an electrical force?

- states that for two charged objects that are much smaller than the distance between them
- the force between them varies directly as the product of their charges and inversely as the square of the separation distance

20

(Forces and Energy Part 2a : Coulomb's Law and Newton's Law of Universal Gravitation)
Compare and contrast Coulomb's law and Newton's law. How are they the same? How are they different?

- similar : they both decrease inversely as a square of distance between charge/mass
- differ : most important difference is that electrical forces (Coulomb) may be either attractive or repulsive, whereas gravitational forces (Newton) are only attractive

21

(Forces and Energy Part 2a : Coulomb's Law and Newton's Law of Universal Gravitation)
What are vector and scalar quantities? Are electrical force and gravitational force vector or scalar?

- vector :
- quantity having direction as well as magnitude
- examples : velocity, force, acceleration, momentum
- scalar :
- quantity having only magnitude, not direction
- examples : speed, pressure, mass, energy, temperature, time, length, area, work
- gravitational force is vector
- electrical force : electric field strength is vector, electric potential is scalar

22

(Forces and Energy Part 2a : Coulomb's Law and Newton's Law of Universal Gravitation)
Describe the inverse-square law (see study sheet for table to fill in)

- SEE PAPER
- a physical law that states a quantity is inversely proportional to square of distance from source of physical quantity

23

(Forces and Energy Part 2a : Coulomb's Law and Newton's Law of Universal Gravitation)
How are Newton's law of universal gravitation and Coulomb's law examples of the inverse square law?

- Newton's Law of Universal Gravity : depends on mass
- Coulomb's Law of Electrical Force : depends on the charge of particles
- both have a denominator of distance squared

24

(Forces and Energy Part 2b : Electricity and Magnetism)
What is magnetic force? What makes an object magnetic?

- are created by moving charges
- happens due to moving charges, spinning in the same direction, electrons spin and revolution produce it

25

(Forces and Energy Part 2b : Electricity and Magnetism)
What is a magnetic field?

- place in space near a magnet or electric current where a physical field is created from a moving electric charge that creates force on another moving electric charge

26

(Forces and Energy Part 2b : Electricity and Magnetism)
How does magnetic force differ from electric force?

- magnetic force : larger when objects are closer, exists only when there is moving electric charge, can only attract
- electric force : larger when objects are closer, exists only when two objects are charger, can repel or attract

27

(Forces and Energy Part 2b : Electricity and Magnetism)
What happens to charged particles in a magnetic field?

- a magnetic field is produced by moving electric charges

28

(Motion)
Describe what the equation F=ma means and how it relates to Newton's second law.

- force (F) = mass of an object (m) x its acceleration (a)
- Newton's second law of motion describes the relationship between an object's mass and the amount of force needed to accelerate it
- the more mass an object has, the more force you need to accelerate it
- the greater the force, the greater the object's acceleration

29

Unit of force

- also called a Newton