5: Forces Flashcards
define the moment of a force.
the turning effect of a force
what is the equation to calculate the moment of a force?
moment of a force (Nm) = (perpendicular) distance (from the pivot to the line of action), in (m) x force (N)
define pivot
the point at which something can rotate or turn, also known as the fulcrum
what are the moments about a pivot like if the object is balanced?
the total anticlockwise moment is equal to the total clockwise moment
what two things can be used to transmit the rotational effects of forces?
a lever; a gear system
what (3 things) do levers have?
a pivot; an effort (force used to move a load over a distance); a load (the overall force exerted, usually by a mass or an object, on a surface)
what are levers?
force multipliers - increase the force acting upon a load, without increasing the effort
how would you increase the force on a load (using a lever)?
use a longer lever to increase the perpendicular distance from the pivot to increase the overall force
what is newton’s second law (using momentum/ momentum change)?
force (N)= momentum change (kgm/s) / time (s)
how can you decrease the force needed to make an object decelerate/accelerate?
decrease the overall momentum change; increase the collision/impact time
what is impact force equal to?
it is equal to the change of momentum per second
what is the centre of mass of an object?
the single point on the object where all of its mass can thought to be concentrated
where is the centre of mass of a regular shaped object?
it is located at the geometric centre
how do you find the centre of mass of an irregular shaped object?
attach a boss and clamp to a retort stand. put the optical pin in the cork and suspend the object from the pin and attaching it to the boss and clamp. also suspend a pendulum bob from the optical pin by using a string. now you can draw a line in line with the string. now do the same, but suspend the object from a different point and draw the line again. the point at which the lines cross is the centre of mass.
what (3 things) do gears do?
transfer the moment of a force (aka torque); change the speed of a turning mechanism; change the axis of rotation - change linear motion into rotation, vice versa
what are the ratios of gears?
ratio of moments = ratio of teeth = ratio of radii
what is the equation for pressure?
pressure (Nmsquared or Pa) = force (N) / area (msquared)
why do sharp scalpels cut more easily than blunt ones?
it has a smaller area of contact so the pressure when the same force is applied is greater, so it has a greater cutting effect.
what happens when a low gear in a car is chosen?
when a low gear is chosen: a small gear wheel driven by the engine shaft is used to turn a large gear wheel on the output shaft - this shaft therefore turns slower than the engine shaft, but the turning effect is greater. low gear gives low speed and a high turning effect.
what happens when a high gear in a car is chosen?
when a high gear is chosen: a large gear wheel driven by the engine shaft is used to turn a large gear wheel on the output shaft - this shaft therefore turns faster than the engine shaft, but the turning effect is lower. high gear gives high speed and a low turning effect.
what is the equation for density?
density (kg/mcubed) = mass (kg) / volume (mcubed)
how does the pressure in a liquid change w depth?
it increases.
what does the pressure of a liquid depend on?
it depends on the density of the liquid - liquids w lower densities have lower pressures.
what is the equation to calculate the pressure at the base of a liquid?
pressure (Pa) = height (m) x density (kg/mcubed) x gravitational field strength (N/kg)
what is the equation to calculate the pressure at the surface of a liquid?
pressure (Pa) = force normal to a surface x area of that surface
