Stationary objects can accelerate , deccelerate or change direction when a reaultant force acts on it.
Without any resultant force, the object is either stationary or moving at constant velocity.
A resultant force is when all the forces acting on the object are added and it is the single force that has the effect as what all the force would do to the object
a=F/m is the equation that shows how acceleration is affected by the Force and mass.
It can also be written as F=ma
F-Force is measured in Newtons (N)
m-Mass is measured in kilograms (kg)
a-Acceleration is measured in metres per second squared (m/s^2)
Speed is different from velocity
Speed is how far an object travels in a given time
Velocity is the speed in a particular direction
Distance time graphs
Slope=constant speed
Flat= stationary
Slope downwards= constant speed back
Curves =Acceleration
Speed= distance/ time
(m/s ) (metres) (Seconds)
v=s/t
Velocity uses the same equation but distance can be negative and different yet travelling the same speed
Velocity time graphs
Slopes = constant acceleration
Flat line = constant speed
Downward slopes = constant deceleration
Curves = changing acceleration
Area of under the line of a velocity time graph represents the distance traveled.
Area of under the line of a velocity time graph represents the distance traveled.
a=(v-u)
____
t
a acceleration (m/s^2)
v-u difference in speed (m/s)
t time (s)
Forces and breaking
Thinking distance and braking distance affects the stopping distance of a car.
When a car travels are constant speed. the resultant force is zero as the force from the engine is balanced by the air resistance and friction,
When a car is traveling at constance speed, every force is balanced by an equal and opposite force.
Force of engine balanced by air resistance + friction
Weight balanced by reaction force of the road.
When a car is speeding up resultant force is not zero.
Force of engine is greater than the resistive forces therefore the car accelerates
When a car slows down the force from the engine is either reduced or the resistive forces has increased e.g. brakes.
Stopping distance = Thinking distance + braking distance
Thinking distance increases if the reaction time increases.
Factors that affect reaction time are:
Tiredness
Distractions
Influence of drugs.
Braking distance is the length a car goes before it halts when the brakes are applied.
It depends on the speed of the car
condition of tyres
road conditions.
Brakes causes a frictional force on the wheel. It reduces the kinetic energy of the vehicle and increases the temperature of the brakes.
Falling objects
Falling objects have different stages.
Object accelerate because of its weight when released, there is a resulting force which goes downwards.
The object keeps accelerating and gains speed but air resistance also increases
Eventually, the object's weight reaches a terminal velocity ( steady speed) cas the weight is balanced by the air resistance.
Lighter objects reaches terminal velocity faster than heavier objects as they have less weight.
On the moon there is no air so no air resistance, when different weight objects are dropped both drop at the same speed.
Velocity time graphs for falling objects
The slope shows initial acceleration
It curves off so it decelerates due to air resistance
It levels off and reaches a terminal velocity.
Weight and mass
W=m * g
W- weight is in Newtons N
m- mass is in kilograms kg
g- gravitational field strength measured in newtons per kilogram, N/kg
the g of the earth is around 10 N/kg
the moon has around 1.6 N/kg
Elasticity
Elastic objects store energy as elastic potential energy.
Work is done on the object to change its shape which stores elastic potential energy.
Hooke's Law
When an elastic object is stretched, the extension is directly proportional to the force applied to it.
F= k * e
F- Force in newtons ,N
k- Spring constant in newtons per metre,N/m
e is extension in metres ,m
In a graph of Force by Extension, the gradient is the spring constant.
There's a limit of portionality where when an object exceeds it, it will change the spring constant of the object permanently.
Thinking distance and braking distance affects the stopping distance of a car.
When a car travels are constant speed. the resultant force is zero as the force from the engine is balanced by the air resistance and friction,
When a car is traveling at constance speed, every force is balanced by an equal and opposite force.
Force of engine balanced by air resistance + friction
Weight balanced by reaction force of the road.
When a car is speeding up resultant force is not zero.
Force of engine is greater than the resistive forces therefore the car accelerates
When a car slows down the force from the engine is either reduced or the resistive forces has increased e.g. brakes.
Stopping distance = Thinking distance + braking distance
Thinking distance increases if the reaction time increases.
Factors that affect reaction time are:
Tiredness
Distractions
Influence of drugs.
Braking distance is the length a car goes before it halts when the brakes are applied.
It depends on the speed of the car
condition of tyres
road conditions.
Brakes causes a frictional force on the wheel. It reduces the kinetic energy of the vehicle and increases the temperature of the brakes.
Falling objects
Falling objects have different stages.
Object accelerate because of its weight when released, there is a resulting force which goes downwards.
The object keeps accelerating and gains speed but air resistance also increases
Eventually, the object's weight reaches a terminal velocity ( steady speed) cas the weight is balanced by the air resistance.
Lighter objects reaches terminal velocity faster than heavier objects as they have less weight.
On the moon there is no air so no air resistance, when different weight objects are dropped both drop at the same speed.
Velocity time graphs for falling objects
The slope shows initial acceleration
It curves off so it decelerates due to air resistance
It levels off and reaches a terminal velocity.
Weight and mass
W=m * g
W- weight is in Newtons N
m- mass is in kilograms kg
g- gravitational field strength measured in newtons per kilogram, N/kg
the g of the earth is around 10 N/kg
the moon has around 1.6 N/kg
Elasticity
Elastic objects store energy as elastic potential energy.
Work is done on the object to change its shape which stores elastic potential energy.
Hooke's Law
When an elastic object is stretched, the extension is directly proportional to the force applied to it.
F= k * e
F- Force in newtons ,N
k- Spring constant in newtons per metre,N/m
e is extension in metres ,m
In a graph of Force by Extension, the gradient is the spring constant.
There's a limit of portionality where when an object exceeds it, it will change the spring constant of the object permanently.
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