Gravity

Gravity

• Newton was the first to make several observations about gravity

• Newton's apple-while watching the apple fall, he had the insight that the same object that pulls the apple to the ground also pulls the moon towards the Earth​

• Why doesn't the Moon crash into the Earth,

• The moon is moving in a pattern that follows the curvature of the Earth​, so it travels in a curve around the earth as a Satellite

Newton's Law of Universal Gravitation

• Everything pulls on everything else through the force of gravity

• The force of Gravity is simple: it only involves Mass and distance

• Law of Universal Gravitation: every mass attracts every other mass with a force that is directly proportional to the product of the interacting masses, and inversely proportional to the square of the distance separating them

• When on Earth, the distance we measure to is the Earth's Center

• Gravity gets weaker the farther apart two masses are

The Universal Constant of Gravitation G

• ​G is the universal constant of Gravitation

• G=6.67 x 10^-11

• Gravity is a very weak force compared to other forces, we feel it so strongly because of the massive size of the Earth​

Ocean Tides

• ​The tides are connected to the moon through the force of Gravity

• As the moon revolves around the Earth, the force of Gravity changes depending on which side of the Earth it is on​

Weight and Weightlessness

• ​Say you are standing on a scale in an elevator

• What forces act on you when the elevator stands still​?

• When the elevator accelerates, the scale would change its reading based on the direction

• If accelerating upwards, the scale has more pressure on it the reading goes up

• If accelerating downwards the pressure decreases and the reading goes down

• If the elevator goes into free fall, the​re is not pressure on the scale and you are in a weightless state

• Weightlessness is ​not the absence of gravity, but the absence of the support force

Projectile Motion

• Gravity causes an object to fall in a curving motion when thrown

• Projectile: any thrown object that continues to move due to inertia​

• Two parts: a vertical component and a horizontal component

• Only the vertical component is affected by gravity

• If you throw one object and drop another object of the same mass at the same time, they will hit the ground at the same time because the force of gravity is the same for both

Satellite

• A satellite is any projectile moving fast enough to fall continuously around the Earth

• To be a satellite the horizontal velocity must be great enough for its falling distance to match the Earth's Curvature

• Satellites have a tangential velocity, parallel to the Earth's Surface​