Astronomy CH 4

Weight

The force that a scale measures when you stand on it, so, weight depends on your mass and the forces (including gravity) acting on your mass.

The only way to change and objects Momentum is to apply a _____ to it

force

Acceleration

When the velocity of something changes in anyway, whether in speed, direction, or both.

Newtons Third Law

Every force is always paired with an equal and opposite reaction force. In astronomy, this tells us that objects always attract EACH OTHER through gravity.

The Universal Law of Gravitation (statement 1)

Every mass attracts every other mass through the force called gravity.

Free-falling

Free-falling without any resistance to slow you down results in you being weightless.

Atmospheric drag

Friction can cause objects to lose orbital energy.

Newtons 2nd law

Mass X Acceleration = Force (F=ma) Tells us what happens to an object when a net force IS present. Astronomically, it tells us stuff like why large planets have greater affect on asteroids and comets than smaller planets like earth.

Conservation of Momentum

Momentum will be the same before and after.

Gravitational encounter

One way for two objects to exchange gravitational energy. Is where they pass close enough to feel the effects of the other's gravity

Bound Orbits

Orbits in which an object goes around another object over and over again.

Unbound Orbits

Paths that bring an object close to another object just once.

Newtons 1st law

States that in the absence of a net force, an object will move with constant velocity. An object at rest (velocity = 0) will remain at rest, and objects in motion tend to remain in motion with no charge in either their speed or direction.

Potential energy

Stored energy

Velocity

Tells us speed and direction.

The Law of Conservation of Angular Momentum

Tells us that Total Angular Momentum can never change. An object can only change angular momentum by transferring some of it to or from another object.

The law of Conservation of Energy

Tells us that, like momentum and angular momentum, energy cannot appear out of nowhere and disappear into nothingness. Objects must exchange energy with each other to gain or lose it.

Acceleration of gravity (g)

The acceleration of a falling object. On earth the rate is 9.8 m/s, assuming no air resistance.

Mass

The amount of matter in an object.

Tidal Force

A difference in attraction that stretches the earth to create two tidal bulges, one facing the moon and one away from the moon.

Angular Momentum

A special type of "Circling Momentum". It's "angular" because an object moving in a circle turns through an angle of 360°.

The Universal Law of Gravitation

All the statements can be summarized in one function: Fg = G((m_1*m_2)/d²) Fg is the force of gravitational attraction M_1 and M_2 are masses of the two objects d is the distance between their centers G is a the Gravitational Constant (G = 6.67 x 10^-11 m³/(kg x s²)

Newtons version of Kepler's third law

Allows us to calculate the mass of a distant object if we measure the orbital period and distance of another object around it (like a moon).

Gravitational Potential Energy

An objects GPE depends on its mass and how far it can fall as a result of gravity. An object has more GPE the higher up it is.

Orbital Angular Momentum

Angular momentum = m*v*r m = mass v = velocity r = orbital radius (at current position)

Rotational Angular Momentum

As long as Earth isn't transferring any of its rotation's angular momentum to another object, it keeps rotating at the same rate. (Earth is actually gradually transferring to the moon).

Mass-energy

Einstein discovered that mass itself is a form of potential energy. E = mc² E is the amount of potential energy m is the mass of the object c is the speed of light

Radiative energy

Energy carried by light.

Kinetic energy

Energy of Motion

Speed

How far something will go in a certain amount of time.

Basic Types of Energy

Kinetic, Radiative, Potential.

Thermal Energy

The kinetic energy of many particles. (subcategory of Kinetic energy) Thermal energy and temperature are not the same thing. thermal energy measures TOTAL kinetic energy of all randomly moving particles in a substance. Temperature measures the AVERAGE kinetic energy of the particles

Escape velocity

The minimum velocity needed to escape planetary orbits. Does not depend on the mass of the escaping object. It does depend on where it starts. Earth's is about 400,000 km/hr or 11 km/s.

Momentum

The product of an objects mass and its velocity. Momentum = Mass x Velocity

Joule

The standard unit of energy in science.

The Universal Law of Gravitation (statement 3)

The strength of gravity between two objects decreases with the square of the distance between their centers. We therefore say gravitational force follows an inverse square law.

The Universal Law of Gravitation (statement 2)

The strength of the gravitational force attracting any two objects is directly proportional to the product of their masses.

Orbital Energy

The sum of an objects kinetic and gravitational energies.

Newtons Laws of Motion

They govern the motion of everything from our daily movements on earth to the movements of planets, stars and galaxies throughout the universe.

Kelvin

Used in science more often than F or C.

Newtons laws reflect deeper aspects of nature known as ___________

conservation laws

The ____ ____ acting on an object represents the combined effect of all the individual forces put together.

net force (overall force) A change in momentum only occurs when netforce is zero.