Air Resistance

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Air resistance is a frictional force that is exerted on objects as they travel through the air and causes them to slow down. It is a force that is described as working in the opposite direction to the forces that cause the movement of the object. It therefore opposes other forces. These forces include gravity. We can see the effects of air resistance in everyday life and how, for example, it causes falling objects to slow down. If we drop a sheet of paper on the floor, or watch leaves falling from the trees in autumn, or a parachutist falling to Earth, we see air resistance in action. As the effects of the force of gravity pull the objects to the earth, there is a counter-acting force or up thrust from the air. This opposing force causes the falling object to slow down, since one of the effects of a force is to make things slow down. Changing the shape of the falling object in some way can change the effect of air resistance. Think again about the parachutist. As he or she freefalls from the aeroplane they are accelerating towards the ground until they reach a terminal velocity (the term used when forces acting on the object are balanced and it falls at a constant velocity) of about 10m/s2. When the parachute opens, their speed is suddenly and greatly reduced as the air fills the opening parachute. The surface area of the parachutist with their parachute has increased thereby increasing the effects of air resistance. The same effect can be demonstrated using two identical pieces of paper, one open, one screwed up. The masses of the sheets of paper both remain the same but they will fall to the ground at different speeds. Because the flat piece has a greater up thrust acting on it, it is subject to greater air resistance and will fall more slowly.

 

man in black jacket and blue pants riding yellow and red parachute

Air resistance is a force that slows down an object as it moves through the air and can be seen as a force that works in the opposite direction to the forces that cause an object to move. So, for example, in the picture of a parachutist the force of gravity is pulling the person towards the Earth whilst the parachute is resisiting this downwards movement, slowing down movement.

Take a look at the video below to see what happens to falling objects when air restistance is removed. Most people think that heavier object fall faster than lighter object, for example a heavy ball and a feather. Without air resistance both fall at the same speed.

Here’s the same experiment carried out by astronaut Dave Scott during the Apollo 15 mission in 1971. The theory that this demonstrates was first developed by Galileo

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