GRAVITY: An attraction to Earth… What stops us from falling off the surface of the Earth? Why is high jump so difficult? Why do we get hit with bird poo? Of coarse the answer is GRAVITY... This is a non-contact force that pulls and attracts objects towards Earth. Without gravity, even the Earth’s atmosphere would float off into space.

Gravity as a force: Mass vs. Weight… The force of gravity is not the same on all objects – the greater the mass of an object, the greater the force of gravity on it. Mass is different to weight. The weight of something or someone is usually equal to the force of gravity pulling it down. The standard unit of force in the newton (N). At the Earth’s surface, the force of gravity is about 10 newtons for every kg of mass. Because the force of gravity is less on Mars, a person weighs less than half their weight on there.

How does gravity Relate to our Megastructures? Gravity was the greatest challenge for the Egyptians as they manually hauled stone to piece together the Pyramids Countless people fell to their deaths during the construction of the Brooklyn Bridge How does gravity Relate to our Megastructures? Gravity has impacted on the Leaning Tower of Pisa, to turn it from a boring old monument, to a world renowned tourist attraction Because of gravity, the Statue of Liberty had to shipped over from France piece by piece and put together in New York Harbor

Falling down… Lets drop a piece of paper... What forces are acting on it??? Gravity is not the only force that acts on falling objects. The way objects fall depends on the total force acting on them, not just the pull of gravity. Air in the atmosphere pushes against all falling objects – this is called AIR RESISTENCE and is an example of fluid friction.

A Practical Example… Answer the following questions: Drop a coin from waist height How many forces are acting on the coin as falls through the air? Drop a coin and a paper disc at the same time Which object landed first? What two forces were acting on the paper disc? What is different about the forces acting on the coin? Drop the coin with the paper on top Which lands first? Why?

Reaching Top Speed… The air resistance on a moving object increases as the object moves faster. What happens to wind when you run or cycle faster? When you go fast, you feel the air pushing against your face, but when you slow down it stops. When an object starts to fall, it moves slowly. There is not much air resistance. As the object speeds up, the air resistance gets much larger. If an object travels fast enough, the air resistance can become as big as the force of gravity on the falling object. Once this happens, the objects stops speeding up and has reached terminal velocity.