# Gravity

## 16 terms

### Weight and Mass

~Weight: a measure of the gravitational force exerted on an object
~Free-Fall Acceleration g=9.8 m/s/s
~F=ma
~Thus, weight is equal to mass times free-fall acceleration
~w=mg

### Weight is measured in newtons

~Weight is a force
~SI unit of weight is the newtons (N)
Ex. 2.25 kg x 9.8 m/s/s=22 N on Earth

### Weight is different from mass

~Mass: a measure of the amount of matter in an object
~Weight is the gravitational force that an object experiences because of its mass
~Earth, where g=9.8 m/s/s
~Venus, where g=8.9 m/s/s
~Mars, where 3.7 m/s/s
~Neptune, where g=11.0 m/s/s

### Weight influences shape

~Gforce affects the shape of living things
~large animals need strong skeleton because they have big mass

### Law of universal Gravitation

~All objects in the universe attract each other through the force of gravity
~As the Gforce decreases as the distance between 2 masses increases
~ The symbol G is constant

### All matter is affected by gravity

~no matter large or small objects, there is a Gforce between them
~the force exerted by something that has small mass, such as paper clip, however, is not noticeable

### Gravitational force increases as mass increases

~gravity is the reason that an apple falls from a tree. When an apple's stem breaks the apple falls down because the Gforce between earth and the apple is much greater than the Gforce between the apple and the tree.

### Gravitational force decreases as distance increases

~When calculating the Gforce between 2 large objects, use the distance between the objects' centers
~G is a very small number

### Free Fall

~Free-fall: the motion of a body where only the force if gravity is acting on the body
~In the absence of air resistance, all objects falling near Earth's surface accelerate at the same rate regardless of their mass

### Free-fall acceleration is constant because of the law of universal gravitation

~The constant G does change at any location
~the distance "d" is about to equal to the radius of earth.
~First mass "m1" is the mass of Earth
~Second mass "m2" the mass of the object near Earth

### Air resistance can balance weight

~falling object stops accelerating when the force of air resistance becomes equal to Gforce on the object (the weight of the object0
~Terminal Velocity: the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

### Astronauts in orbit are in free fall

~Astronauts in orbit are actually quite near Earth and are certainly not weightless

### Projectile Motion

~projectile motion: the curved path that an object follows when thrown, launched, or otherwise projected near the surface of earth
~Projectile motion has two components--horizontal and vertical. When the two motions are combined, they form a curved path

### Projectile motion has a horizontal component

~Component: a part of something
~ignoring air resistance, when it is small, allows one to simplify projectile motion

### Projectile motion also has a vertical component

~When you throw a ball, gravity pulls it downward, which gives the ball vertical motion

### Orbiting is projectile motion

~An object is said to be orbiting when it is traveling in a circular or nearly circular path around another object.
~When a spaceship orbits earth, it is moving forward but it is also in free fall toward Earth