- Written by Nadia O'Carroll
What is gravity? Each particle of matter attracts every other particle, the force is proportional to the mass of, and the distance between the objects. Massive bodies such as planets exert very powerful forces .The Earth is surrounded by a gravitational field which exerts a force of attraction on other objects.
When an object on Earth is situated on a hard surface, there is an upward contact force that balances the downward gravitational force; the force on the mass of the object is its weight.
When there is no contact force to oppose the gravitational force the object falls freely and is pulled towards the surface of the Earth. The gravitational pull causes an object to accelerate at a constant rate of 9.8metres per second, for each second of the descent.
Even when an object is falling freely downwards, there are upward restraining forces such as air resistance and these are called drag forces. As an object continues to increase its velocity downwards, the drag also increases, at a certain point the drag force and gravitational force become equal and the object stops accelerating and moves at a constant velocity called terminal velocity.
When the falling object collides with the surface of the Earth an impact force will be experienced, but the dynamics of the collision can be influenced by a number of factors eg soft surface.
Despite the force of gravity, many creatures spend their lives in mid air seemingly defying this powerful force.
Birds, bats, reptiles and insects use the force of drag and lift to counter the force of gravity, some species can only glide but others such as birds, insects and bats can both glide and fly.
In gliding, wings push air downward and by Newtons Third Law an opposite force pushes the wings upward, which supports and slows the descent.
In flying, wings act as an aerofoil and are flapped and rotated to create both lift and thrust. To avoid pushing air backwards when they flap their wings, most wing movement is angled so the motion is similar to rowing in the sky.
Insects fly by rotating or whirling their wings in a figure 8 pattern that acts as a propeller. They can move their wings at up to 1000 beats per second – the fastest known muscles.
Many plants rely on the wind to disperse their seeds and may have all manner of adaptations for flying –gliders, parachutes, helicopter and spinners are all types of seeds adaptations.