pressure and moments Flashcards
(19 cards)
what is a moment
the turning effect of a force
the moment depends on two things:
- size of the force
- distance from the pivot at which the force acts
what is the equation for a moment
moment (Nm) = force (N) x perpendicular distance from pivot (m)
what unit are moments measured in?
- newton metres (Nm)
- newton centimetres (Ncm)
what is the principle/law of moments?
the sum of the clockwise moment equals the sum of the anti-clockwise moment for an object to be in equilibrium
what is the wheelbarrow example?
the wheelbarrow with a bigger wheel is best because it has a bigger surface area so the force is more spread out meaning the pressure is less on the mud
what is the chair example?
the chair leaves marks because it has a smaller surface area (the stands) so the force is more concentrated, meaning it has a higher pressure on the carpet
what is pressure?
pressure is a measure of how much force there is per unit area
what is the equation for pressure?
pressure = force/area
what unit is pressure measured in?
- N/m(2) = Pascal
- N/cm(2)
to maximise pressure, you use a:
small area, like a knife and fork
to minimise pressure , you use a:
large area, like a truck with large tyres
how do i find out my pressure?
weight = w
area of one shoe = a
pressure = force / area
a x 2 = 2a
pressure = w/2a N/m(2) or N/cm(2)
if i lift one foot off the ground, what happens to my pressure?
it doubles, as there is less surface area
how does pressure of the air work?
air particles move about and collide with surfaces. collisions exert a force on the surface area which gives you a pressure.
how does the egg in a bottle example work? (pressure of the air)
there is high pressure outside
there is low pressure inside
the burning paper uses up oxygen which decreases pressure inside, so the high pressure outside pushes the egg in
how does the straw in a bottle example work ( pressure of the air)
low pressure outside
high pressure inside
you blow air into the bottle, which increases pressure inside and pushes water up and out
how does the jug with holes example work?
( pressure and depth)
pressure increases with depth
- greater weight of water (or maybe air) presses down on the water underneath it
how does the bag with holes example work? (pressure and direction)
water comes out equally in all directions. pressure is the same in all directions
