motion and forces Flashcards
(23 cards)
what is the difference between a scalar and vector quantity
vector quantities have a direction and magnitude
scalar quantities only have a magnitude
give examples of each quantity
vector: force, velocity, displacement, weight, acceleration, momentum
scalar: time, speed, distance, mass, energy, temperature
give the equation relating speed distance and time
d = sxt
typical speeds for walking, running and a car in a built up area
w = 1.4m/s r = 3m/s c = 13m/s
define acceleration in terms of velocity and time
acceleration is the change in velocity in a certain amount of time
give the equation for average acceleration
a = (v-u) / t
what does the gradient represent for a distance/time graph
gradient at any point gives the speed of the object
what does the gradient represent for a velocity/time graph
gradient = acceleration
how would you find the distance travelled by an object from it’s velocity/time graph
area under any section of the graph = distance travelled in that time interval
state newton’s first and second laws of motion
first law: a resultant force is needed to make something start moving, speed up or slow down
second law: resultant force = mass x acceleration
( acceleration is inversely proportional to
mass)
explain why cars have safety features to reduce decelerations experienced by passengers
- large decelerations can cause serious injuries
- this is because large deceleration requires large force
- the force can be lowered by slowing the object down over a longer time
- safety features are designed to increase collision times which reduce the force and reduce risk of injury
- eg. seat belts stretch slightly, air bags slow you down and crumple zones allow the front and back of a vehicle to crumple up easily in a collison, increasing the time taken to stop
what is the formula for calculating the weight of an object
weight = mass x gravitational field strength
what is the force acting to produce circular motion
centripetal force
explain why there must be a force acting to produce circular motion
- velocity is both the speed and direction of an object
- if an object is travelling in a circle ( constant speed) it is constantly changing direction therefore constantly changing velocity
- this means it’s accelerating
- this means there must be a resultant force acting on it
describe an experiment to investigate newton’s second law of motion
- via the motion of a trolley on a ramp
- measure the mass of the trolley, the unit masses and the hanging hook - also measure the length of a piece of card which will interrupt the light gate beams
- adjust the height of the ramp until the trolley just starts to move
- mark a line on the ramp just before the first light gate to ensure the trolley travels at the same distance every time
- attach trolley to hanging masses , hold still at the start line and then let go
- each light gate will record the times
- acceleration can then be found via (v-u)/t
what is inertia
the tendency for motion to remain unchanged
what is newton’s third law of motion
when two objects interact, the forces they exert on each other are equal and opposite
eg. if you push a trolley, the trolley will push back against you just as hard
state the formula used to calculate an object’s momentum
momentum = mass x velocity
explain the link between newton’s third law and conservation of momentum
- for example snooker balls
- before collision the white ball has a momentum of 0.6kgm/s
- red ball has a momentum of zero
- total momentum is 0.6 kgm/s
- when they collide, the white ball exerts a force on the red ball causing it to begin moving.
- due to newton’s third law, the red ball also exerts an equal but opposite force on the white ball
- this force causes the white ball to slow down
- the collision lasts 0.1 s
- after the collision, the white ball continues moving at 1 m/s, the red begins at 3 m/s
- momentum has been conserved
what is meant by a person’s reaction time
the time between noticing the hazard and applying the brakes / action
describe an experiment to measure reaction time
- the ruler drop experiment
- sit with your arm resting on the edge of the table
- get someone else to hold a ruler to hang between your thumb and forefinger lined up with zero
- without any warning, the person drops the ruler
- close thumb and finger to catch as quickly as possible
- measurement is at the point it was caught
- longer the distance, longer the reaction time
state two factors that affect the thinking difference for a stopping car
- reaction time
- speed
state four things that can affect braking distance of a vehicle
- speed
- car mass
- brake condition
- friction between tyres and road
