P2.1 Forces and their effect Flashcards
What is a resultant force?
When a number of forces acting at a point may be replaced by a single force that has the same effect on the motion as the original forces all acting together
What does a resultant force cause?
a change in an object velocity
What will happen to a stationary object if the resultant force acting on it is 0?
The object will remain stationary
What will happen to a stationary object if the resultant force acting on it is not 0?
The object will accelerate in the direction of the resultant force
What will happen to a moving object if the resultant force acting on it is 0?
The object will continue to move at the same speed and in the same direction
What will happen to a moving object if the resultant force acting on it is not 0?
The object will accelerate in the direction of the resultant force
Whenever 2 objects interact, the forces they exert on each other are…
equal and opposite
What is the acceleration of an object determined by?
the resultant force acting on the object and the mass of the object
In the equation to find acceleration what are the units for
F= m x a ?
F- resultant force in newtons (N)
m- mass in kilograms (Kg)
a- acceleration in meters per second squared (m/s2)
What does the gradient of a distant time graph represent?
Speed
What is speed and velocity measured in?
m/s
What is the difference between velocity and speed?
Speed is just how fast something is going with no regard to direction
Velocity must also have the direction specified
On a distance time graph, what do the flat sections show?
that the object has stopped moving
On a distance time graph, what do the straight uphill or downhill sections mean?
that the object is travelling at a STEADY SPEED
On a distance time graph, what do downhill sections mean?
That the object is going back towards its starting point
On a distance time graph, what does a steepening curve mean?
the object is accelerating
On a distance time graph, what does a levelling off curve mean?
the object is decelerating
In the equation to find acceleration
a= v-u (divided by) t
what does each letter stand for and what are the units?
a- acceleration (m/s2)
v- final velocity (m/s)
u- initial velocity (m/s)
t- time taken (s)
What is acceleration?
how quickly velocity is changing (can be a change in speed and/or a change in direction)
In a velocity time graph, what does the gradient represent?
acceleration
In a velocity time graph, what do flat sections represent?
an object moving at a steady speed
In a velocity time graph, the steeper the gradient…
the greater the acceleration or deceleration
In a velocity time graph, what do uphill sections represent?
acceleration
In a velocity time graph, what do downhill sections represent?
deceleration
In a velocity time graph, how do you find out the distant travelled by an object in a time interval?
Work out the area under the graph for that time period
When a vehicle travels at a steady speed, the resistive forces balance the…
driving force
The greater the speed of a vehicle the greater the……….. needed to stop it in a certain distance
braking force
What is the stopping distance of a vehicle?
the sum of the thinking distance and breaking distance
What is the thinking distance?
the distance a vehicle travels during the drivers reaction time
What is the breaking distance?
The distance a vehicle travels under the breaking force
What factors affect a drivers thinking distance?
how fast the driver is going
tiredness
drugs and alcohol
distractions
What happens when a car’s brakes are applied?
work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the breaks increases.
What factors affect a vehicles breaking distance?
How fast the vehicle is going
How good the breaks are
How good the tyres are
Weather conditions
Road surface
Give some examples of adverse road conditions
wet or icy conditions
The faster an object moves through a fluid (liquid or gas) ……
the greater the frictional force that acts on it
Describe how and why the speed of a falling object such as a parachuter changes
When object first starts to fall, the force of gravity is much more than the frictional force slowing them down so they accelerate.
As the speed increases, the grater the frictional force (air resistance) that acts on it.
This reduces the acceleration until the frictional force is equal to the accelerating force. It will have reached its maximum speed (terminal velocity) and will fall at a stead speed.
Eventually, the object’s weight is balanced by the air resistance. There is no resultant force and the object reaches a steady speed, called the terminal velocity
What is terminal velocity?
when the frictional force is equal to the accelerating force. This means the object will not be able to accelerate anymore.
it will have reached its maximum speed (terminal velocity)
In the equation to find the wight of an object
W= m x g
what do each of the letters stand for and what are the units?
W- weight in newtons (N)
m- mass (kg)
g- gravitational field strength per kilogram (N/kg)
A force acting on an object may cause a change in…
shape of the object
What may a force applied to an elastic object such as a spring result in?
the object stretching and storing elastic potential energy
What is an elastic object?
an object that can go back to its original shape after a force has been removed
What is elastic potential energy converted into when the force is removed from an elastic object?
kinetic energy
The extension of an elastic object is……….. to the force applied, provided that the limit of proportionality is not exceeded.
directly proportional
In the equation
F= k x e
what do the letters stand for and what are the units?
F- force (N)
k- spring constant (N/m) (value depends on the material you are stretching)
e- extension (m)
How can a vehicle be altered to increase the vehicle’s top speed?
more powerful engine
aerodynamic (streamline)- minimises air resistance
How would the braking distance change if the road was wet?
it would increase
Explain why a bigger current is taken from the batteries when a scooter goes uphill
more power is needed
because work is done against gravity
Why does the acceleration of an aircraft decrease as it moves along the runway even though the force of the engines is constant?
Because as speed increases, air resistance increases
this reduces the resultant force
Why does a parachutist reach terminal velocity and why does opening the parachute reduce terminal velocity?
- on leaving the plane, the only force acting is gravity
- as parachutist falls air resistance acts upwards
- gravity is greater than resultant force
- as velocity increases so does air resistance
- terminal velocity is reached when air resistance = gravity
- opening parachute increases surface area so increases air resistance
- Air resistance is bigger than gravity
- so parachutist decelerates
- the lower velocity means reduced air resistance
- air resistance and weight become equal but at a lower terminal velocity
How would a car becoming more streamline affect its speed?
air resistance is smaller
so it reaches a higher speed
When a vehicle travels, what are most of the resistive forces caused by?
Air resistance
does acceleration increase or decrease if the mass of a moving object increases?
decreases
What is the weight of an object?
a force which depends on the mass of the object and the gravity acting on it
What is gravity measured in?
N/kg
When a spring is stretched, what is the extension?
the difference between the original length and the stretched length
Explain why the force on the water produced by the engine propeller of a boat causes the boat to move
as it produces a force from the water on the boat
in the forward direction
Explain why applying the breaks of the car causes the temperature of the breaks to increase
work is done by friction between the brake and wheel
which causes a decrease in kinetic energy and increase in heat energy
Explain why a stationary skateboard moves backwards when a skateboarder jumps off it
exam answer—learn!
momentum before jumping = momentum after jumping
before jumping momentum of skateboard and skateboarder is 0
after jumping, skateboarder has momentum forwards so skateboard must have equal momentum backwards
