Forces and Motion Flashcards
force
the action of one body on a second body
air resistance
friction acting on an object moving through air
friction
the force that acts when two surfaces rub over one another
drag
friction that acts on an object as it moves through a fluid
gravity
the force that exists between any two objects with mass
terminal velocity
the greatest velocity reached by an object when moving through a fluid
gravitational field formula
weight/mass
equation connecting force, mass and acceleration
force = mass x acceleration
momentum formula
momentum = mass x velocity
impulse formula
force x time for which the force acts
resultant force formula
change in momentum/time
impulse
the change in an objects momentum
resultant force
the sum of all forces acting on an object
turning effect
when a force causes an object to rotate if there were no resistive forces
pivot
the fixed point about which a lever turns
moment
the turning effect of a force about a pivot
moment formula
force x perpendicular distance
When is an object in equilibrium
forces are balanced, turning effects must also be balanced
equilibrium
when no net force or net moment act on a body
principle of moments
when an object is in equilibrium the sum of the anticlockwise moments is equal to the sum of clockwise moments about the same point
centre of gravity
when all the mass of an object is said to concentrated at one point
lamina
flat 2D shape
equation linking resultant force and momentum
change in momentum/time = resultant force
what is the principle of conservation of momentum
momentum is always conserved in an explosion/collision, so there is no net change in momentum
momentum before = momentum after (provided there are no external forces)
the time taken for the change in momentum to occur is proportional to the..
resultant force felt by the object
reaction force
the upwards force from a surface in opposition to an objects weight
energy
the ability to do work
pressure in fluids formula
density x gravitational field strength x height
why when moving in a cicrular horizontal path the resultant force points towards the center of the circle?
centripetial force
(force/acceleration towards centre of circle)
acceleration formula
change in velocity/time
newtons 1st law
object either remains at rest or continues in a straight line at constant speed unless acted on by a resultant force
spring constant formula
k = F/x
limit of proportionality
the extension that Hooke’s law no longer applies to - the extension is no longer proportional to the force
describe an object in circular motion
- speed increases as force increases, with mass and radius constant
- radius decreases if force increases, with mass and speed constant
- an increased mass requires an increased force to maintain radius and speed
5 examples of energy stores
kinetic, GPE, chemical, elastic, electrostatic
kinetic energy formula
1/2mv^2
GPE formula
mgh
mechanical work done
the amount of force needed to move an object a certain distance
mechanical work done formula
W = fd
efficiency formula
useful energy ouput/total energy input x 100
or
useful power onput/total power input x 100
pressure
force per unit area, P = F/a
Man made things that use moments
Crowbar, wrench, door, tap, spanner, scissors
