forces and motion Flashcards
average speed formula
average speed=distance/time
acceleration
the rate of change in velocity
acceleration formulas
a= v-u/t
a=v2-u2/2s (distance) (suvat)
important note about acceleration
change in direction is still acceleration
vector quantities
- velocity
- displacement
- force
- acceleration
- momentum
scalar quantities
- speed
- distance
- mass
- energy
- density
difference between scalar and vector
scalar= magnitude (size)
vector= magnitude AND DIRECTION
velocity formula
v=s/t
how forces can affect bodies
- change their shape
- change their speed
- change their direction
weight
the name given to the force of gravity on a mass
electrostatic force
the force between two charges
thrust
the force pushing an object forward
air resistance
the friction of the air on a moving object
upthrust
the force of a fluid pushing on an object
compression
forces that are squashing an object
tension
forces that are stretching an object
normal reaction force
a force due to contact between two objects
force formula
force=mass x acceleration
f=ma
relationship between force and acceleration
directly proportional
gradient of force, acceleration graph: f/a=m
relationship between acceleration and mass
inversely proportional
stopping distance
stopping distance=thinking distance + braking distance
factors affecting thinking distance
- intoxication
- distractions (e.g mobile phones)
- tiredness
factors affecting braking distance
- condition of tyres and brakes
- condition of road and weather
- mass of vehicle (heavier=takes longer to stop)
thinking distance
distance a vehicle travels in the time it takes for a driver to react to a situation and apply the brakes
braking distance
the distance a vehicle takes to stop once the driver has applied the brakes
terminal velocity
the maximum velocity an object can reach as it falls through a fluid
weight formula
weight= m x g
why g is smaller on the moon than on earth
the moon has a lower density and lower mass
hooke’s law
the extension of a spring is directly proportional to the force applied
hooke’s law force formula
force=extension x spring constant
elastic limit
- material no longer shows elastic behavior
- material is permanently deformed
elastic bands
elastic bands do not obey hooke’s law because the extension is NOT directly proportional to the force applied
momentum formula
momentum=mass x velocity
P=m x v
momentum conservation
the momentum before is equal to the momentum after in any collision or explosion provided no external forces act on the system
elastic collisions
when objects don’t stick together after the collision
elastic collision equation
m1u1+- m2u2= +-m1v1+-m2v2
plastic collision
when the objects stick together after the collision
plastic collision equation
m1u1+-m2u2= v(m1+m2)
isolated system
no external forces acting on the system
force
the rate of change in momentum
force and momentum formula
F=ΔP/t
principle of moments
for a system to be balanced the sum of clockwise moments must be equal to the sum of anti-clockwise moments
moment formula
moment= force x perpendicular distance from pivot
car safety
- crumple zones
- air bags
- side bars
- collapsable steering wheels
- designed to increase the time taken for a driver or passanger to change momentum because F=
newtons 3 laws
- an object will not change its motion unless a force acts on it
- f=mass x acceleration
- whenever two objects interact, they exert equal and opposite forces on each other
