Motion and Forces Flashcards
In a distance time graph what does it mean if the line is moving at a constant speed in a straight line that slips upwards?
It is moving at a constant speed
What does the gradient of a distance-time graph show?
Represents the objects speed
How can you tell velocity from speed?
Velocity is speed in a given direction
How can you tell from a distance time graph that the object is stationary?
Stationary is a horizontal line
Unit of acceleration?
m/s (squared)
What does the area under the line on a velocity time graph represent?
The distance travelled
If the velocity time graph is a horizontal line what is the acceleration?
0 acceleration
What can forces do?
A force can change the shape of an object or its state
What’s the unit for force?
N (Newtons)
If the resultant force on an object is zero what happens?
The object stays at a constant velocity
If the resultant force on an object is not zero what happens?
The velocity of the object will change
What is acceleration?
The change in velocity (speed) per second
What is the driving force ( engine force/motive force) down to?
It is due to friction between the ground and the tyre of each drive wheel
What is the resultant force?
A single force that has the same effect as all the forces acting on an object
What happens if the resultant force of an object isn’t zero?
The velocity will change
When does the velocity of an object increase ? What type of acceleration is it ?
If the resultant force is in the same direction as the velocity it increases
Positive acceleration
When does the velocity of an object decrease ? What type of acceleration is it ?
If the resultant force is in the opposite direction as its velocity
Negative acceleration
If the resultant force is big what happens to the acceleration?
The acceleration is greater
If the mass of an object is great what happens to the acceleration?
It is smaller for a given force
What two forces are opposite to the driving force of a car?
Friction
Air resistance
What two factors affect the stopping distance?
Thinking distance
Braking distance
What is the thinking distance?
The distance travelled by the vehicle in the time it takes the driver to react
What factors increase the thinking distance?5
Tiredness
Alcohol
Drugs
Mobile phone use
Increasing the speed
How can you work out the thinking distance?
when you are given the drivers reaction time and speed
cars speed x reaction time
What is the breaking distance?
The distance travelled by the vehicle during the time the braking force acts
What increases the breaking distance?
Poor weather conditions
Poor car maintenance e.g. Worn tires
If the speed increases
What is the weight of an object?
The force of gravity on it
What do weight measured in?
N
What is mass?
The quantity of matter in it
What is mass measured in?
KG
How much gravitational field strength does the earth have?
Roughly 10 N/Kg
What is the unit of gravitational field strength?
N/Kg
What increases drag force?
Speed
What happens when an object falls in a fluid?
The fluid drags on the object
What happens when an object falls through the air?
The drag force is air resistance
What happens to the acceleration of an object and why?
The acceleration of the object decreases as it falls
because the drag force increases as it speeds up
When does an object reach a constant velocity (speed)? & what is its name?
When the drag force on it is equal and opposite to the weight
Terminal velocity
If the resultant force is zero what is the acceleration?
Zero too
What type of component shows a change in temperature?
A thermistor
Why would the current passing through each element be the same?
It is a series circuit and therefore the current is the same throughout
Because of forces, explain why the parachutist reached a terminal velocity and why opening the parachute reduces the terminal velocity?
1 when he left the airplane the force acts downwards
2 as the parachutist falls air resistance acts upwards
3 the weight is greater than the air resistance
4 as the velocity and speed equal eachother he reached terminal velocity
5 opening the parachute increased his surface area increasing the air resistance
6 air resistance is greater than the weight
7 the resultant forces slow down and when they are equal he reaches terminal velocity
What does the mass of an object have to do with its acceleration?
The greater the mass the smaller acceleration
What are the opposite forces of the driving force of a car?
Friction and air resistance
What is the unit of gravitational field strength?
N/kg
What increased drag force?
Speed
When an object falls through the air what force is acting on it?
Air resistance
When an object falls describe the torces?
The drag force increase as it speed up
Acceleration decreases
When the drag force is equal and opposite to the weight what happens?
Terminal velocity : the resultant force is zero so the acceleration is 0
What name is given to the constant speed?
Terminal velocity
Why would it be good for electricans to wear rubber soled boots?
Increases overall resistances
So gives a smaller current in the event of electric shock
When will the resultant force acting on an object cause an object to move?
When it is not zero the object will accelerate in the direction of the force
What happens if the result force acting on a stationary object is zero?
It will remain stationary
What happens if the resultant force acting on a moving object is zero?
The object will continue to move at the same speed and in the same direction
What is acceleration measured in?
m/s2
What determines the acceleration of the object?
The resultant force acting on it
The mass of it
What are most resistive forces caused by?
Air resistance
What is happening (in terms of force) when a vehicle travels at a steady speed?
The resistive forces balance the driving force
What does an increased speed do to the breaking force needed?
Increase it
If you are given braking force, what does increased speed so to the stopping distance?
Increases it
What is the stopping distance?
Thinking distance add braking distance
What is thinking distance?
The sum of the distance the vehicle travels during the drives reaction time
What is the braking distance?
The distance the car travels under the braking forc
What is braking distance affected by?
Poor condition of car brakes or three
Wet or icy weather or road conditions
Describe the process of breaking?
In terms of energy and force.
When brakes applied,
The friction force between the brakes and the wheel
Reduces the kinetic energy of the vehicle
The temperature of the brakes increase
In a fluid, as speed increases, what happens to frictions?
The greater the frictional force that acts on it
Describe what happens when an object falls through a liquid?
It initially accelerates due to the force of gravity
Eventually, the resultant force will be zero
The object will move at its terminal velocity (constant speed)
What is gravitational field strength measured in?
N/kg
What happens if force is applied to an elastic object?
The object stretches
And stores elastic potential energy
What is Spring constant measured in?
N/m
What is the extension of an elastic object directly proportional to?
(Given the limit of proportionality is not exceeded)
The force applied
What is work done measured in?
J
How can long distance vehicles check that their drives don’t drive for too long?
Tachographs
What is deceleration?
Negative acceleration
What forces act when a crate is pushed along the floor?
Push force (as a person exerts force on crate) Friction (between the floor and the crate)
When a crate is pushed along the floor, when will the resultant velocity be zero?
When it is pushed at a constant velocity
Push force on the crate is equal in size but acts in the opposite direction to the force of friction of the floor on the crate
Describe the forces of a jet plane taking off?
The thrust force (engine force) of the engine is GREATER than the force of air resistance (drag force) on it
Resultant force on it is different to the thrust force and the force of air resistance
Resultant force is therefore not zero
Greater the force the quicker the takeoff
Describe the force changes when a car drives applies the brakes?
The braking force is greater than the force from the engine
Resultant force is different between braking and engine force
Breaking force acts in the opposite direction
So it slows the car down
If an object is acted on by two unequal forces acting in opposite directions, what is the resultant force?
Equal to the difference between the two forces
In the direction of the larger force
When does velocity decrease?
The resultant force is in the opposite direction to its velocity
When does velocity increase?
If the resultant force is in the same direction as the velocity
What are the resistive forces acting on a car?
Friction (between parts of the car and the tyre and road) and air resistance
What does the accelerator pedal do?
Varies the driving force
What is the stopping distance?
The shortest distance a vehicle can safely stop in
Things that affect thinking distance?
Tiredness
Alcohol
Drugs
Mobile phones
Increase reaction times
Things that affect breaking distance?
Poorly maintain vehicles - longer to stop as brakes and tyres are less effective eg worn brakes or tyres
Adverse road conditions - brake with less force to avoid skidding eg icy or wet roads
Faster a vehicle is travelling - further it travels before it stops
What affect both thinking and stopping distance?
Speed of vehicle
What happens when an object is released above ground and falls?
It accelerates downwards at a constant acceleration of 10 m/s2
Acceleration due to gravity
What happens if an object falls with no other forces acting on it?
The resultant force on it is its weight
How is drag force increased?
Speed
Describe the changes in forces and velocity as an object falls through a liquid?
Acceleration decreases as it falls
As drag force increases as it speeds up
Resultant force decreases so acceleration decreases
Reaches terminal velocity when drag force equals its weight
Resultant force is zero so the acceleration is zero
When does a parachutist reach terminal velocity?
Drag force equals force of gravity
How do anti skid surfaces work?
They increase the friction between the vehicle and the grounds so that more force can be applied without skidding happening
So stopping distance is reduced
When a vehicle is travelling at high speed what force is greater?
Air resistance (drag force)
How do wind deflectors work?
Reduce air resistance on vehicle
So less engine force and power needed to maintain a speed
Fuel costs reduced
(As speed increases so does air resistance)
Describe how skidding happens?
Brakes applied with too much force
Wheels lock and tyres slid on the road as a result
What does an LED do?
Emits light when a current passes through it
What does a diode do?
Allows current to move only in one direction
What does a resistor do?
Limits the current in a circuit
What does a variable resistor do?
Allows the current to be varied
What does a fuse do?
Melts and breaks the circuit if the current through it is greater than a certain amount
What does a cell (battery) do?
A cell is necessary to push electrons around a complete circuit
A battery consists of two or more cells
What does an indicator do?
Emits light as a signal when a current passes through it
Or as a light source such as a bulb
Why does resistance in a metal increase as temperature increases?
The ions in metal vibrate more
So they twist the passage of electrons through the filament more
Why is the force needing to pull a boat force is greater than the resultant force?
Resistant forces are needed to overcome
When potential difference increases, why would the resistance of a bulb increase?
Temperature of bulb increases
Why do control rods reduce the amount of energy released each second from a nuclear fuel?
They absorb excess neutrons
So there are fewer chain reactions
Chain reactions slow down
Why does applying the breaks on a car cause the temperature to increase?
Friction between the brakes and the whelk
Decrease in kinetic energy and increase in thermal energy
Describe why a cyclist would rapidly accelerate then at a lower acceleration?
Forward force more than air resistance
Velocity increased
Air resistance increases (as speed increases)
Resultant force decreases
Cyclist still accelerates with less velocity
WHAT CAUSES AIR RESISTANCE TO INCREASE
MORE VELOCITY
What causes a cyclist to gradually reach terminal velocity?
Air resistance increase Velocity decrease Forces become equal Zero resultant force Zero acceleration Terminal velocity
What happens to the breaks when the kinetic energy of the bike decrease?
Temperature increases
Describe the general for anything that becomes charged?
Friction between objects
Charge transfers between objects
What is an ion?
An atom that has lost/gained electrons
