What if…..

I know you are probably familiar with the movie “Gravity.” A lot of that was scientifically accurate. I find it interesting, however, that the entire movie was about the lack of gravity rather than gravity.

So what is gravity? Gravity is defined as an attractive force between any two objects. Its strength depends on: 1. the mass of the objects 2. the distance between them The force increases if objects have a greater mass and/or are closer together.

Humans exert a gravitational force! We just aren’t big enough to pull any objects towards us.

Law of Universal Gravitation

This law was used to find the planet Neptune. After Uranus was discovered in the 1840’s, it was thought that its orbit was being affected by another planet. It turns out that this was true, and the planet beyond Uranus was named Neptune.

Free Fall When all forces except gravity on a falling object are small enough to be ignored, we say the object is in free fall. On Earth, the acceleration of a falling object in free fall is 9.8 m/s 2.

Force of Earth’s Gravity Equation Force of gravity (N) = mass (kg) x acceleration of gravity (m/s 2 ) OR F= mg For example, A skydiver with a mass of 60 kg would have a force of 588N: F = 60 kg x 9.8 m/s 2 = 588N

Weight vs. Mass Weight and mass are not the same. Weight is a force and mass is a measure of how much matter there is in an object. Weight increases as mass increases. However, while weight is affected by gravity, mass is not. For example, on the moon your mass would not change, but your weight would decrease. Why?

Because of this relationship between weight and gravity, we can say: W = mg

Weightlessness and Free Fall

Do all objects fall at the same rate?

Projectile Motion Have you ever noticed that thrown objects don’t always travel in straight lines? They arc. This is because of Earth’ gravity causing objects to follow a curved path.

Centripetal Force This is acceleration toward the center of a curved or circular path, like in a merry-go- round. Centripetal force is the net force exerted towards the center of the curved path.

Gravity can be a centripetal force