Allison Thompson Chapter 4 notes

chapter 4

***How so were describe motion?
-Speed
*rate at which objects move
-Velocity
* speed and direction
-Acceleration
* any change in velocity.
Acceleration
*All falling objects accelerate not counting friction of air resistance

*Galileo showed that g is They same for all falling objects regardless of mass.

*Momentum is mass x velocity

*A net force changes momentum which generally means acceleration (change in velocity)

*They rotational momentum of a spinning or orbiting object known as angular momentum.


thought question

Is net force acting on each of  They following?
1. A car coming to a stop. Yes
2. A bus speeding up. Yes
3. A elevator moving up at a constant speed. No
4. A bicycle going around a curve. Yes
5. A moon orbiting Jupiter. Yes

**How is mass different from weight?
Mass
-the amount if matter in an object
Weight
- The amount of force that acts on an object.
 Thought question
On the moon your weight is less, but your mass is the  same.

Why are astronauts weightless in space?
-There is gravity in space
- Weightlessness is due to constant state of free-fall.




Chapter 4.2

*How did Newton change our view if the universe?
 He realized the same physical laws that operate on Earth also operate in the heaven
He discovered laws of motion and gravity
 Much more: Experiments with light first reflecting telescope calculus....

Newton's laws of motion
1. An object moves at constant velocity unless a net force acts to change its speed or direction.
2.Force = mass x acceleration
3.For every force there is always an equal and opposite reaction force.

though question

Is the force the earth exerts on you larger, smaller, or the smae as the force ypu exerts on it?
 Earth and you exert equal and opposite forces on each other.

A compact car and a large truck have a head-on collision. Are the following questions true or false?
1. The force of the car on the truck is equal and opposite to the force of the truck on the car. True
2. The momentum transferred from the truck to the car is equal and opposite to the momentum transfered from car to truck. True
3. the change of velocity of the car is the same as change of velocity of the truck. False.


Chapter 4.3
 *what keeps a planet rotating and orbiting the sun?
 Conservation of momentum
 Total momentum of interacting objects cannot change unless an external force is acting on them.
 Interacting objects exchange momentum through equal and opposite forces.

*What keeps a planet rotating and orbiting the sun?
angular momentum= mass x velocity x radius
 The angular momentum of an object cannot change unless an external twisting force (torque)

*Where do objects get their energy?
Energy makes matter move.
energy is conserved but I can....
-transfer from one object to another

Kinetic (motion)
Radiative (light)
Stored or potential
**energy can be Stored but not destroyed **

Thermal Energy
*thermal energy is related to temperature but is NOT the same. temperature is the average Kinetic energy of the particles in substances.
*thermal energy is a measure of the Kinetic energy of all the particles in a substance. it therefore depends on both density and temperature.

gravitational potential energy.
 On earth it depends on....
*an objects mass
*strength of gravity
* distance an object could potentially fall.

in space an object or gas cloud has more gravitational energy when it is spread out than when it contracts.
a contracting cloud converts gravitational potential energy to thermal energy.

Mass-Energy
*Mass itself is a form of potential energy.
 a small amount of mass can release a great deal of energy.
concentrated energy can spontaneously turn into particles.

Conservation of energy
*energy can be neither created nor destroyed


chapter 4.4
*What determines the strength of gravity?
The universal law of gravitation
1.every mass attracts every other mass.
2.Attraction is directly proportional to the product of their masses
3.Attraction is inversely proportional to square of the distance between their centers

*Kepler's first two laws applied to all objects not just planets
*ellipses are not only orbital paths. Orbits can be bound or unbound.
*Newton generalized Kepler,s third law
*if  a small object Orbits a large one and you measure the objects.

*How do gravity and energy together allow us to understand Orbits
 Total orbital energy stays constant if there is no external force
orbit cannot spontaneously change

*Friction and atmospheric drag can change orbit. Also gravitational encounters.
*Escape velocity
If an object gains enough orbital energy it may Escape

How does gravity cause tides?
The moon's gravity pulls harder on near side of earth than on far side.
The difference in the moon's gravitational pull stretches earth.

Tides and Phases
-size of tides depends on the phase of the moon
Tidal Friction gradually slows earths rotation
Moon once orbited faster; tidal Friction caused it to lock in synchronous rotation