topic 5 - forces Flashcards
What is moment?
the turning effect of a force
What is equation to calculate moment?
moment (Nm) = force (N) x distance (m)
How is the distance measured in moments?
the perpendicular distance from the pivot to the line of action of the force
if an object is in equilibrium, what can be said about the moments acting on the object?
the sum of the clockwise moment about the pivot is equal to the sum of the anticlockwise moment about the pivot
What is the function of a lever?
A lever allows us to lift a heavy object by applying a relatively small amount of force
Explain how a lever can act as a force multiplier
- Force is applied further from the pivot.
- Using a lever means less force is needed to get the same moment
Describe what a gear is and what function it serves in machinery.
A gear is a circular disc with teeth
- in machinery, it is interlocked with other gears in order to transmit the rotational effects of a force from one place to another
what is a fluid?
either a liquid or a gas
in any fluid, at what angle do the forces due to pressure act on a given surface?
pressure in fluids causes a force normal (at right angles) to any surface
what is the equation for pressure?
pressure = force/area
what happens to the density of the atmosphere with increasing altitude?
At increasing altitudes, density decreases
why does atmospheric pressure decrease with an increase in height?
- the pressure is created by collisions of air molecules
- the quantity of molecules decreases as the height increases
- this means atmospheric pressure decreases with an increase of height
what is the Earth’s atmosphere?
a thin layer of air around the earth
How does the pressure in fluids increase with depth?
- as the depth increases, the mass of liquid above that depth also increases
- this means that the force is due to the mass increase
- since the force has increased whilst the area has remained constant
why does the pressure in fluids increase with density?
- As the density of a fluid increases, the number of particles in a given volume increases
- consequently, the weight of the fluid is greater
- this means that the force from the fluid above a certain point is larger. Since the force has increased, the pressure also increases
what equation shows the magnitude of pressure in liquids at different depths?
pressure = height x density x gravitational field strength
what is upthrust always equal to?
the weight of the fluid that the object displaces
what factors influence whether an object will sink or float?
- upthrust
- weight
- density of fluid
what is the equation used to calculate an object’s moment?
moment = mass x velocity
what is the unit used for momentum?
kgm/s
what is meant by “momentum is conserved”?
total momentum before = total momentum after
what is the equation for change in momentum?
change in momentum = force x time
how does a seatbelt improve a passenger’s safety during a collision?
- passenger must decelerate from the vehicle’s velocity at impact to zero, meaning they undergo a fixed change of momentum
- the force they experience is equal to the rate of change of momentum
- seatbelts increase the time over which the force is applied, reducing the rate of change of momentum and therefore reducing the force experienced
why is momentum not always conserved in a collision?
external forces may act on the object too
