# Gravity and Resistance

#### There is the famous story of how Newton, a famous physicists and mathematician in the 1600s discovered gravity, which is what we are studying here today. He was sitting under an apple tree when an apple dropped and hit him on the head, which led to the question, what make objects fall to the ground? Gravity was discovered. We know that gravity is what keeps us on the ground and without gravity, we would be floating out of the Earth's atmosphere. Gravity causes any two objects to be drawn to each other. So in the case of the falling apple, the apple was attracted to the ground. Although there were others before Newton who noted that gravity existed, Newton was the first to come up with an explaination of why it happens.

#### Newton's theory of gravity said that gravity acts on all matter and is dependant on the mass of the objects and the distance between them. The force of attraction was directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

#### Galileo, an Italian scientist also did a very famous experiment from the leaning tower of Pisa to demonstrate that objects do not fall faster because of their masses because the time of descent is independent of mass. He dropped two balls of different mass at the same time from the top of the building and both objects landed simultaneously at the bottom. He showed that all objects fell to the ground at a constant acceleration, the acceleration of gravity. This disproved the Greek philosopher and scientist Aristotle's theory of gravity where he stated that objects fall at a speed relative to their mass.

Gravity

Newton's Laws

Video

F= mg (Force of gravity is equal to mass times acceleration of gravity which is 9.8m/s^2)

These three fundamental physics formulas are fall displayed in the video. For more information about what is happening or how these equations work or come into play, click on the "discussions" button above for more information.

F= (1/2)ρ(v^2)CA (Air resistance force is equal to one half times the density of the fluid rho, times the speed of the objecct v squared, times the drag coefficient C and times the cross sectional area A)

Newton's second law states that F=ma which means that the force is equal to the mass of the object times the acceleration. There is only movement in the object when there are unbalanced forces.

Air Resistance

VIDEO 1: video taken from youtube of a man on the moon dropping a ball and a feather (https://www.youtube.com/watch?v=5C5_dOEyAfk)