3 - Forces and Motion Flashcards
What is the difference between a vector and scalar quantity?
A vector quantity is a quantity with both magnitude and direction (e.g. velocity, displacement, force). A scalar only has a magnitude (e..g. speed, distance).
How is displacement different to distance?
Displacement is the distance travelled in relation to the starting point in one straight line whereas distance is the total distance travelled, where direction is not considered.
Flat line on dt graph
object stationary
Straight sloping lines on dt graph
object travelling at constant speed (steeper = faster)
gradient of dt graph
velocity
flat line on vt graph
constant velocity
straight sloping lines on vt graph
constant acceleration (steeper = the faster the object is speeding up or slowing down)
gradient of vt graph
acceleration
area under vt graph
distance travelled (displacement)
Stopping distance
the distance a vehicle will travel between the moment a danger is spotted to when the vehicle has completely stopped (sum of thinking and braking distance)
Thinking distance
distance travelled between when the driver sees the danger to when they first apply the brakes
Braking distance
distance travelled between when the driver applies the brakes to when the vehicle has fully stopped
Factors affecting thinking distance
speed, drugs, alcohol, tiredness, distractions
Factors affecting thinking distance
speed, drugs, alcohol, tiredness, distractions
Factors affecting braking distance
speed, mass, condition of brakes, tyre conditions (e.g. pressure), road conditions (e.g. slope, ice, gravel, weather), aerodynamics of car
Thinking distance proportionality
Thinking distance ∝ speed (d=st so d∝s, W=Fd so E (energy transferred) = Fst so E∝s)
Braking distance proportionality
Braking distance ∝ speed^2 (E=0.5mv^2 so E∝v^2)
Journey of skydiver
At the start of his jump the air resistance is small so he accelerates downwards.As his speed increases his air resistance will increase. Eventually the air resistance will be big enough to balance the skydiver’s weight. At this point the forces are balanced so his speed becomes constant this is called TERMINAL VELOCITY. When he opens his parachute the air resistance suddenly increases, causing him to start slowing down. Because he is slowing down his air resistance will decrease again until it balances his weight. The skydiver has now reached a new, lower terminal velocity
As speed increases, air resistance…
increases
Horizontal motion in projectile qs
Air resistance is assumed to have no effect on horizontal motion so horizontal acceleration is 0
