Chapter 4 Quiz: Olivia Ward

1. How do we describe motion?
   Motion is described through speed, velocity, and acceleration. Speed is the rate at which objects move. Speed and a change in direction is known as velocity. Acceleration is any change in velocity.
2. 
   How is mass different from weight?
   Mass is the amount of matter in an object while weight is the force that acts on that object. For example, on the Moon, objects have their same mass as on Earth, but their weight changes because of the difference in gravity. On the Moon, a hammer and a feather fall at the same rate.
3. 
   How did Newton change our view of the universe?
   Newton discovered that the same physical laws that apply to Earth also apply to the 'heavens' (space / the universe), laws of motion and gravity, and conducted experiments with optics, the first reflecting telescope, and calculus.
   
   
4. What are Newton's three laws of motion?
   Newton's first law states that an object moves at a constant velocity unless a net force changes its speed or its direction. His second law is the equation, force = mass X acceleration. His third law states that for every force, there is always an equal and opposite reaction force.
5. 
   What keeps a planet rotating and orbiting the Sun?
   The momentum of interacting objects cannot change unless an external force is acting on it. An object's angular momentum cannot be changed unless an external twisting force is effecting it. Therefore, a planet's momentum cannot change unless an external force changes its orbiting pattern.
6. 
   Where do objects get their energy?
   Energy is conserved and it can be transferred from one object to another. Energy can change type but cannot be destroyed. Objects can have kinetic energy, radiative energy, potential energy, thermal energy, gravitational potential energy, or mass energy.
   
7. 
   What determines the strength of gravity?
   The strength of gravity depends on the object's mass. Every mass attracts other masses. Attraction is directly proportional to the product of their mass. Attraction is inversely proportional to the square of the distance between their centers.
   
   
8. How does Newton's law of gravity extend Kepler's laws?
   Kepler's first two laws apply to all orbiting objects, not just planets. Orbits can be ellipses, parabolas, or hyperbolas. Newton generalized Kepler's third law. If a small object orbits a larger object and you measure the orbiting object's orbital period as well as its distance, you can calculate the mass of the larger object.
   
9. How do gravity and energy allow us to understand orbits?
   Total orbital energy stays constant if there are no external forces affecting the orbit. Orbits cannot spontaneously change. The orbit of an object cannot change without energy being transferred.
   
10. How does gravity cause tides?
    The Moon's gravity pulls harder on the near side of the Earth compared to the far side of the Earth. The difference in the Moon's gravitational pull stretches the Earth. The size of the tides ultimately depend on the the phase of the Moon.