Chapter 4 Quiz: Jessica Horn

How do we describe motion? Speed is the rate at which an object is moving. Velocity is speed in a certain direction. Acceleration is a change in velocity, meaning a change in either speed or direction. Momentum is mass x velocity. A force can change an object's momentum, causing it to accelerate. 

How is mass different from weight? An object's mass is the same no matter where it is located, but its weight varies with the strength of gravity or other forces acting on the object. An object becomes weightless when its free-falling, even though the mass remains unchanged. 

How did Newton change our view of the universe? Newton showed that the same physical laws that operate on Earth also operating in the heavens, making it possible to learn about the universe by studying physical laws on Earth. 

What are Newton's three laws of motion? 1. An object moves at constant velocity if there is no net force acting upon it. 2. Force = mass  acceleration. 3. For any force, there is always an equal and opposite reaction force. 

What keeps a planet rotating and orbiting the Sun? Conservation of angular momentum means that a planet's rotation and orbit cannot change unless it transfers angular momentum to another object. The planets in our solar system do not exchange substantial angular momentum with each other or anything else, so their orbits and rotation rates remain steady. 

Where do objects get their energy? Energy is always conserved, for it can never be created nor destroyed. Objects received whatever energy they now have from exchanges of energy with other objects. Energy comes in three basic categories: kinetic, radiative, and potential. 

What determines the strength of gravity? According to the universal law of gravitation, every object attracts every other object with a gravitational force that is directly proportional to the product of the objects' masses and declines with the square of the distance between their centers. 

How does Newton's law of gravity extend Kepler's laws? 1. Newton showed that Kepler's first two laws apply to all orbiting objects, not just planets. 2. He showed that elliptical bound orbits are not the only possible orbital shape, orbits can also be unbound (taking the shape of a new parabola or a hyperbola). 3. Newton's version of Kepler's third law allows us to calculate the masses of orbiting objects from their orbital periods and distances. 

How do gravity and energy allow us to understand orbits? Gravity determines orbits, and an object cannot change its orbit unless it gains or loses orbital energy, the sum of its kinetic and gravitational potential energy, through energy transfer with other objects. If an object gains enough orbital energy, it may achieve escape velocity and leave the gravitational influence of the object it was orbiting. 

How does gravity cause tides? The Moon's gravity creates a tidal force that stretches Earth along the Earth-Moon line, causing Earth to bulge both toward and away from the Moon. Earth's rotation carries us through the two bulges each day, giving us two daily high tides and two daily low tides.                                            Information retrieved from textbook/notes