Gravity

Gravity

King City Astronomy 1AST-1

Zoë Buck

• Newton’s Laws and the concept of FORCE– Inertia: an object in motion stays in

motion– Force = mass x acceleration– Every action has an equal and

opposite reaction• Newton saw a connection between the

motion of a falling apple and the Moon – that they are both governed by the same force

Review of what we know about motion:

• Acceleration: a change in the velocity of an object

• Force: something that causes an acceleration

Newton’s Laws

1. An object’s velocity will not change unless acted on by an external force

2. Force on an object is determined by the acceleration of the object, and the mass of that object (F=ma)

2. Every action has an equal and opposite reaction

Gravity depends on MASS

Acceleration of Gravity

F = M * a OR Fg

= M * g

Acceleration due to gravity is NOT the same as the force of gravity between 2 objects. It is the acceleration felt by the second object due to the first, or vice-versa.

(M is the mass of the person or object, and a is the acceleration due to gravity, which we call g)

On the surface of Earth, g is always the same. This means that when something falls on Earth, no matter WHAT IT WEIGHS, it accelerates at the same speed, so everything falls at the same rate.

Gravity

• The UNIVERSAL LAW OF GRAVITATION

• Fg= m * g

• g=(G*M)/r² • (where G = G= 6.67 *10-11 N(m/kg)²)• So… Fg

= (G * M * m)/ r²

Newton and the Apple

Free Fall

Is there gravity in space?

• Zero Gravity DOESN’T EXIST!

• Microgravity

Free Fall + Velocity = Orbit

Gravity and the Universe

• Gravity is responsible for holding the Earth in its orbit around the Sun


• Gravity is responsible for holding the Sun in its orbit around the Milky Way


• Gravity is responsible for holding the Milky Way in its path within the Local Group


• Gravity is responsible for holding the Earth in its orbit around the Sun, the Sun in its orbit around the Milky Way, and the Milky Way in its path within the Local Group…it is the force that dictates the structure of the Universe

Gravity makes stars and galaxies

The Most Important Things about GRAVITY

• Gravity is what makes things fall toward the Earth (not “down”, but “toward the Earth”)

• Gravity keeps things in orbit (Satellites, Moon, Earth, Sun) – things in orbit are essentially “falling” toward the center of mass of the system

• Gravity is a force between two objects – both objects fall toward each other

• The force of gravity between two objects depends on their MASS (bigger = more gravity), and the DISTANCE between them (farther = more gravity)

• Gravity drives the formation of galaxy clusters, galaxies, stars, and planetary systems

• Therefore gravity determines the structure of the Universe

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Gravity