physics forces/motion and energy resources

acceleration w/ words

rate of change of VELOCITY (including change of direction)

conservation of momentum

total momentum of a system before an event is equal to the total momentum of the system after the event

hooke’s law extension formula

K =

e =

f = Ke

crumple zone

vehicle safety feature that crumples during a collision. it increases the time over which the momentum change occurs, so reduces the force experienced by passengers

elastic deformation

a non-permanent deformation for which the object will return to its original shape when the deforming forces are removed

elastic limit

the force beyond which an object will no longer deform elastically, and will instead deform plastically (permanently)

hooke’s law

the extension of a spring is directly proportional to the force applied to it, up to the limit of proportionality. The constant is the spring constant.

typical human reaction time

150-300 milliseconds, 0.2-0.9 seconds

limit of proportionality

the point beyond which the extension of an elastic object is no longer directly proportional to the force applied to it

define moment no formula ** not momentum

the turning effect of a force

newton’s first law

if a stationary object’s net force is zero, the object will remain stationary. If a moving object’s net force is zero, the object will continue to move at a constant velocity (same speed/direction)

newton’s second law

f = ma
unbalanced forces have an effect on motion

newton’s third law

when two bodies interact, they apply forces to one another that are equal in magnitude, opposite in direction, and of the same type.

non-contact force

a force that acts on an object at a distance - no physical contact, acts through a field

plastic deformation

a permanent deformation for which the object will no longer return to its original shape when the deforming forces are removed

principle of moments

the sum of the clockwise moments about any point must be equal to the sum of anticlockwise moments about the same point

scalar quantities

only have a magnitude (no direction)

seat belt

vehicle safety device that increases the time over which the momentum change occurs during a collision, reduces the force experienced by the wearer.

spring constant

measure of the spring’s stiffness. The higher the spring constant, the smaller the extension is for a given force. given in N/m

stopping distance

thinking distance + braking distance

terminal velocity

maximum velocity an object can reach when falling through a fluid. It occurs when the resistive forces (e.g. air resistance) equal the object’s weight

thinking distance

distance a vehicle travels during the driver’s reaction time. affected by tiredness, drugs, alcohol.

vector quantity

both a magnitude and a direction

chemical energy

a store of energy found in things like batteries, fuels and food

conservation of energy

energy cannot be created or destroyed, only transferred, stored or dissipated

elastic potential energy

story of energy that stretched or compressed objects contain

lubrication

application of a lubricant to reduce the friction that acts between surfaces (like oil)

power

rate at which energy is transferred, rate at which work is done

work done

when a force causes it to move through a distance

formula - distance

distance = speed/time

formula, units momentum

p = mv

momentum (kgm/s) = mass (kg) x velocity (m/s)

formula, units force, accel

F = ma

Fnet (N) = mass(kg) x acceleration (m/s²)

formula - weight

W = mg

weight (N) = mass (kg) x gravitational field strength (9.18N/kg)

force using momentum formula

F = delta P / delta T

Force (N) = change in momentum (kgm/s) / time (s)

formula - moment

M = Fd

moment (Nm) = force (N) x perpendicular distance of force to pivot (m)

formula work done

w = Fd

work done (J) = force (N) x distance moved (m)

work done is equal to…

energy transferred

formula - gravitational potential energy GPE

GPE = mgh

GPE (J) = mass (kg) x gravitational field strength (N) x height (m)

formula - kinetic energy

KE = ½ mv²

kinetic energy (J) = ½ x mass (kg) x velocity² (m²/s²)

gpe and work done and ke equivalent

GPE = KE = work done

formula - power

P = W/t

power (W)= work done (J) / time (s)

formula - accel, distance, speed

v² = u² + 2as

2 examples scalar quantities

mass, distance

2 examples vector quantities

velocity, displacement

if forces are unbalanced, the object will change velocity t/f?

true

if the dependent variable is directly proportional to the independent variable, the graph will look like:

a straight line that goes through the origin

elastic

returns to original shape when stretching force is removed

plastic/inelastic

object remains stretched/doesn’t return to origin shape

is momentum a vector, why?

yes, needs a defined direction (e.g right +, or left -)

factors affecting thinking distance

reaction time: drugs, tiredness, distracted

factors affecting braking distance

friction: road conditions, tyre and brakes condition