Forces+in+action





=__Under Pressure__=  • Air exerts a pressure equally in all directions. The pressure of the atmosphere is due to the weight of the air above us.  • At sea level atmospheric pressure is 100 000 N/m 2 or 100 000 pascals. This is a large number, so we can also say 100 kN/m 2 or 100 kPa or 1 **atmosphere** of pressure.  • This air pressure is about the same as a __ **double-decker bus standing on every square metre** __.  • We are not crushed by the enormous pressure of air because the pressure inside our bodies exactly matches the air pressure outside our bodies.  __Moments__ A lever can be used to apply a force which turns something around a pivot. This is called **the turning effect** or **moment** of the force. The moment is calculated by:

moment of the force = force ´ distance from the pivot (newton metres, Nm) (newtons, N) (metres, m)

If there are several forces on an object, it is in **equilibrium** if the moments of all the forces are balanced. Apparatus