Forces and Motion Flashcards
Speed equation
(m/s) = distance (m) / time (s)
s = d / t
Speed vs Velocity
Speed is scalar (only magnitude)
Velocity is a vector (magnitude and direction)
Scalar examples
speed
temperature
energy
Vector examples
velocity
force
acceleration
Acceleration equation
(m/s2) = change in velocity(m/s) / time (s)
a = v-u / t
velocity time graphs
area under graph = distance travelled
x axis = time
y axis = velocity
Distance vs Displacement
Distance is a measurement of the total path travelled.
Displacement is the straight line measurement between the starting and finishing point.
Final speed equation (v2)
initial speed (u2) + 2 x acceleration x displacement
v2 = u2 +2as
Forces
Gravity
Tension
Friction
Air resistance
Reaction Force
Thrust
Force of gravity (weight)
pulls an object towards the centre of a large mass
Tension
a force in a rope or cable being pulled
Friction
a counter force caused when two objects rub together
Air Resistance
a counter force produced whan an object travels through air
Reaction force / normal
the upward force from a surface to counter weight
Thrust
a pushing force (e.g. by an engine/rocket)
Balanced Forces
Stationary
Constant speed in same direction
Unbalanced Forces
Speed up
Slow down
Change direction
Change shape
Force equation (N)
Mass (kg) x Acceleration (m/s2)
F = M*A
Weight equation (N)
Mass (kg) x Gravitational field strength (N/Kg)
W = m*g
Terminal velocity
- Start, air resistance 0, acceleration downwards
- As speed increases, air resistance also increases
- Eventually, forces will balance, constant speed. (Terminal Velocity)
- When opens parachute, air resistance increases, slows down
- As slows down, air resistance decreases, until balances with weight
- New, lower, terminal velocity.
Stopping distance
thinking distance + breaking distance
Factors affecting thinking distance
alcohol/drugs
age
tiredness
distracted
Factors affecting breaking distance
- condition of brakes
- condition of tyres
- condition of road (wet / icy)
- speed of car
- mass of car
Hooke’s Law
- Extension directly proportional to Force until elastic limit
- When load is removed, the material springs back to its original length
- If the spring excceeds the elastic limit, plastic deformation will occur
Plastic vs Elastic deformation
Elastic - object WILL return to its shape
Plastic - object WILL NOT return to its shape
Materials which not obey hooke’s law
rubber
Force vs. Extension graph
Force (y axis)
Extension (x axis)
