P10 - Force And Motion✔️ Flashcards
Equation for resultant force?
Resultant force = mass x acceleration
F = m x a
What does Newtons second law state?
States that the acceleration of an object is poportional to the resultant force on the object and inversley proportional to the mass of the object
What is inertia?
Inertia is the tendency of an object to stay at rest or continue in uniform motion
-can be defined as: force / aceleration
What is the inertia mass of an object?
Is a measure of the difficulty of changing the objects velocity
Greater resultant force on a object ……?
The greater the objects acceleration
The greater the mass of an object ……?
The smaller its acceleration for a given force
What is weight?
Weight - weight of an object is the force acting on it due to gravity measured in newtons,N
What is mass?
Mass of an object depends on the quantity of matter in it - measured in kilograms,kg
What is gravitational field strength?
Way of measuring how much gravity there is at a single point - strength at earths surface is about 9.8 N/kg
Equation for weight?
Weight = mass x gravitational field strength
W = m x g
What is terminal velocity?
Steady speed achieved by an object freely falling through a gas or liquid - where the frictional force on it is equal to its weight - resultant force is 0
What is the resultant force on an object moving at terminal velocity?
Resultant foce on the object is zero
What is stopping distance?
The shortest distance in which a vehicle can safetly stop - it is the sum of thinking distance and braking distance
What is thinking distance?
Distance traveld by a vehicle in the time it takes the driver to react - proportional to the speed
What is breaking distance?
Distance travelled by a vehicle during the time the braking force acts
Equation for stopping distance?
Stopping distance = thinking distance + breaking distance
Factors affecting stopping distance?
-tirdness,acholl,drugs - increase reaction time because they affect the brain
-faster a vehicle is travelling - further it travels before its stops
-condition of vehicle - worn break/tires take longer to stop they are less effective
-conditions of enviorment - icy road less friction on tires
What is momentum?
Momentum - vector quantity of motion that is made up of the amount of matter moved and the velocity at which it moves
Equation of momentum?
Momentum of moving object = mass x velocity
P = m x v
Measure in kg/ms
What is a closed system?
A system at which the total momentum before an event is the same as the total momentum after the event - called conservation of momentum
Why does making the impact time longer reduce the imapact force?
If an object hits a soft wall, the wall would act as a cushion and increase the impact time so the momentum of the object would be reduced over a longer time and so the change of momentum per second would be less - longer impact time the more the impact force is reduced
What determines the force of the impact when vehicles collide?
Depends on the mass,change in velocity and the length of the impact time
What happens when two vehicles collide - refer to forces?
-They exert equal and opposite forces on each other
-their total momentum is unchanged
Equation for impact force?
Impact force = change of momentum / impact time
Why are safety helmets worn?
They increase the impact time which reduces the rate of which momentum changes per second - so they reduce impact forcce of the impact
Why are seat belts worn?
-time taken to stop someone in the car is longer so the decelerating force is reduced
-seat belt spreads the force out across the chest
What do air bags do?
Spreads the force of an impact across the upper part of a persons body it also increases the impact time so the efect of the force is reduced
Three methods used to reduce impact time in cars?
-collapsible steering wheels
-crumple zones
-side impact bars
Relationship between thinking distance and speed?
Thinking distance is proportional to speed
Factors that effect human reaction time?
Drugs,alcohol and tiredness
Define what an elastic object is?
An object is elastic if it returns to its original shape when the forces deforming it are removed
What is extenstion?
Extenstion is the difference between the length of the object and its original length
Define Hooke’s law?
Extenstion of a spring is directly proportional to the force applied to it, as long as the limit of proportionality is not exceeded.This relationship is linear
Equation for hookes law?
Force applied (F) = spring constant (K) x extenstion (e)
