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Flight. Brainstorm. Gravity vs. Drag. Two things affect the descent rate of an object falling through air: Gravity. Wind resistance (drag). These two forces act together, one pulling the object towards the earth, the other slowing it down. Terminal Velocity. Did You Know?
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Gravity vs. Drag • Two things affect the descent rate of an object falling through air: • Gravity. • Wind resistance (drag). • These two forces act together, one pulling the object towards the earth, the other slowing it down.
Terminal Velocity Did You Know? The terminal velocity for a human being is 200 km/h! The balance of the two results in a maximum rate of descent. Drag Gravity
Gravity vs. Lift • Sir Isaac Newton, an English scientist, observed the force of gravity when he was sitting under a tree and an apple fell on his head! • Gravity is a strong force that pulls everything down toward the center of earth. Therefore, no matter where we stand on Earth, we will not fall off. • The more mass, the more gravity pulls. The lighter the object the less lift required to make it buoyant (able to float in air).
Lift is the upward force used to overcome gravity and to achieve flight. • Lift occurs if the force on the bottom of an object is greater than the force of gravity from above. • To sustain a particular height, lift must equal gravity).
Laws of Flight 1) Bernoulil’s Law of Pressure: The faster air flows, the less pressure it has. • When air is moving, It creates areas of high pressure and areas of low pressure. Fast moving air creates an area of low pressure because the particles are spread further apart while high pressure air has particles packed closer together.
2) Law of Flight: Objects always go from high pressure to low pressure. • A good example of this happens when a hole is made in the body of a passenger plane. The air in the plane is under high pressure to keep passengers comfortable compared to the low pressure air outside. When a hole is made in the body of the plane, objects in the high pressure plane move violently towards the low pressure air outside often resulting in disaster.
3) Newton’s Third Law: This law says that if there Is a force in one direction, there is an equal force In the opposite direction. • For example, when a person on a skateboard pushes backwards on the ground, they move forward. This law helps to explain how rockets and jet engines work.
Parachute • A parachute, with its large canopy, creates a great deal of resistance, causing the terminal velocity to be significantly reduced. • This allows a sky diver to parachute safely to the ground. • The best shape to reduce terminal velocity is a concave shape. • This shape traps the air inside reducing TV.
Parachute • While the concave traps air, however, air has a difficult time escaping from the concave. • As a result, the air tries to escape out one side and then the other, causing it to wobble. • To solve this problem, a small hole is in the center of the concave to allow air to escape, resulting in a smooth descent.
Hot Air Balloons • Hot air balloons operate on Archimedes Principle which states that objects suspended in a fluid (such as a boat in water or a balloon in air) have a buoyant force equal to the weight of the fluid displaced.
Hot Air Balloons • They must have a large envelope. • Normally, but don’t necessarily have a concave shape. • They must dispense hot air every 30 seconds to remain airborne. • In hot air balloons, the heated air expands, filling the envelope. • Heated expanded air weighs less by volume than cooler air. • As a result, heated air will rise above the cooler air.
Hot Air Balloons • To allow for a quick descent, a Velcro vent at the top of the balloon can be opened by means of a rope, speedily dispelling warm air. • This allows the pilot to control the up and down movement of the balloon. • In the air, the hot air balloon’s lateral movement is at the mercy of the prevailing winds.
Airplanes • Roll: The plane rocking from side to side (wing tip up or down) along the longitudinal axis. • Yaw: The nose of the plane swinging left or right along the vertical axis. • Pitch: The plane teetering up and down (nose to tail) along the lateral axis.
Airplanes • In order to achieve a successful flight, gravity, thrust, lift and drag must be in balance. The center of lift and center of gravity must be in balance as well. • The center of lift is the point at which a plane’s total lift seems to be concentrated. • The center of gravity is the point at which the mass of the plane seems to be concentrated.
Jet Engine • Air is taken in through the front of the engine and compress it into a small space. The compressed air is mixed with fuel and burned. The hot air and fuel expand creating a jet of hot gases which are shot out of the rear of the engine. The action of the hot gases being forced from the rear of the plane causes a reaction on the plane which moves it in the opposite direction. • This is an illustration of Newton’s Third Law of Motion. For every action, there is an equal and opposite reaction.
