FORCES AND PRESSURE

Is defined as force acting per unit area

Unit for pressure is N m-2 or pascal (Pa)

1) An elephant weighing 30000 N . The area of one foot in contact with the ground is 15000 cm2.Calculate the pressure it exerts on the floor.

P = F A = 30000 N =5000 N m-2 15000X4x10-4 m2

2)The wind pressure on the wall is 200 Pa.If the wall has an area of 8m2,what is the force on it?

Pressure= Force Area200 Pa = Force 8m2

Force =200 Pa x 8 m2 =1600 N

Why the duck able move smoothly without its feet being stuck in the mud, while the hen is unable to do so?Show your calculation and explain this situation based on pressure concept.

- the webbed feet of duck provide a large surface area of contact between the feet and muddy ground.So the,duck exerts a smaller pressure on the mud compared to the pressure exerted by the hen.Therefore,the duck is able to move smoothly on the muddy ground while the hen is unable to do so.

Which shoe will cause the most pain when tread on our foot?

Shoe A has the largest area of contact with our foot.Shoe D has the smallest area of contact with our footTherefore,shoe D will exert the most pressure on our foot.So our foot feels most painful if trod by shoe D

Force ,pressure

Contact area ,pressure

Force ,pressure

Contact area ,pressure

A student pressing a thumbtack into a piece of wood with a force of 20 N. The surface area of the head of the thumbtack is 1 cm2 and the cross-sectional area of the tip of the thumbtack is 0.01 cm2.Calculate:(a) the pressure exerted by the students thumb on the head of the thumbtack(b) the pressure of the tip of the thumbtack on the wood.(c)What conclusion can be drawn from your answers to (a) and (b)