PAT0640-ABED: Lesson 3 Page 1

Any object that flies through the air must overcome the force of gravity. Gravity is the force that pulls every object downwards. In order for an object to fly, an upward force must be applied to the object that is stronger than the force of gravity. Recall that both air and water are fluids that behave in similar ways. Flying objects must use the properties of air to allow them to lift upwards against the force of gravity.

Note: Sometimes the words weight and gravity are used interchangeably. Weight is the force of gravity acting on an object. Be aware of this subtle difference as you work through this unit.

Objects can overcome gravity by using

Lift, which is producing an upward force using air pressure or currents

Example: Wings

Buoyancy, which means becoming less dense (or lighter) than the surrounding air

Example: Blimps & Hot Air Balloons

Propulsion, which involves using an engine to produce an upward or forward force

Example: rockets or jets

Notebook: How can the force of gravity be overcome?

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Basics of Gravity
In which direction does gravity pull?	Down (towards the centre of Earth)
How can a balloon float in air?	Balloon must be less dense than air; it must be filled with a gas that is less dense than the air around it.
How can you float in water?	You are less dense than water is.
How can an airplane float in air? (Name the extra force needed.)	Wings produce lift.

		LIFT	BUOYANCY	PROPULSION
1.	bird wings	X		X
2.	inner tube floating on water		X
3.	jet engine			X
4.	hang gliders	X
5.	paper airplane	X
6.	hot air balloon		X
7.	rocket			X
8.	boat		X
9.	propeller			X