chapter 4 Flashcards
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 * 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 it is in free-fall, even though its mass is unchanged.
How did Newton change our view of the universe?
Newton showed that the same physical laws that operate on Earth also operate in the heavens, making it possible to learn about the universe by studying physical laws onEarth.
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) F=ma (3) For any force, there is always an equal and opposite reaction force.
Why do objects move at constant velocity if no force acts on them?
Conservation of momentum means that an object’s momentum cannot change unless the object transfers momentum to or from other objects. When no force is present, no momentum can be transferred so an object must maintain its speed and direction.
What keeps a planet rotating and orbiting the Sun?
Conservation of angular momentum means that a planet’s rotation and orbit cannot change unless the planet 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 fairly steady.
Where do objects get their energy?
Energy is always conserved—it can be neither 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?
The universal law of gravitation states that every object attracts every other object with a gravitational force that is proportional to the product of the objects’ masses and declines with the square of the distance between their centers: F = G((m1*m1)/d^2)
How does Newton’s law of gravity extend Kepler’s laws?
(1) Newton showed that any object going around another object will obey Kepler’s first two laws. (2) He showed that elliptical bound orbits are not the only possible orbital shape—orbits can also be unbound in the shape of parabolas or hyperbolas. (3) He showed that two objects actually orbit their common center of mass. (4) 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 energies—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. Tidal forces also lead to tidal friction, which is gradually slowing Earth’s rotation and explains the synchronous rotation of the Moon.
Why do all objects fall at the same rate?
Newton’s equations show that the acceleration of gravity is independent of the mass of a falling object, so all objects fall at the same rate.
