FORCES Flashcards
What is a vector quantity?
Direction and magnitude
What is a scalar quantity?
Magnitude only
How are vector quantities usually represented by?
An arrow showing direction and length shows magnitude
What are some examples of vector quantities?
Force
Velocity
Displacement
Acceleration
Momentum
What are some examples of scalar quantities?
Speed
Distance
Mass
Temperature
Time
What are contact forces?
Have to be touching for a force to act (e.g. friction, air resistance)
What are non-contact forces?
Don’t have to be touching for force to act (e.g. gravitational force, electrostatic force)
What is an interaction pair?
A pair of forces that are equal and opposite and act on two interacting objects
What is mass?
The amount of stuff in an object
What is weight?
The force acting on an object due to gravity
What does the weight of an object depend on?
The strength of the gravitational field at the location of the object
What is the relationship between mass and weight?
They are directly proportional
What does a free-body diagram show
All the forces acting on an isolated object
Size of arrows shows the relative magnitude of the forces
Also shows direction
What is the resultant force of an object?
Add forces going in the same direction
Subtract ones going in different direction
(along the same line)
What happens when a force acts on an object?
Work is done to move the object so energy is transferred from one store to another
How do you convert joules to newton metres?
1J = 1Nm
How do you calculate resultant forces using scale drawings?
Draw forces (North however many cm then East)
Calculate the line (triangle) between them starting from where the force started
What happens when all the forces acting on an object equal 0?
The object is in equilibrium
How do you find the single force of a force acting at an awkward angle?
Draw the components at right angles to each other
Horizontal and vertical component then work out line connecting them
What can an object do if it has been elastically deformed?
It can go back to its original shape and length after the force has been removed
What happens when work is done and an object is stretched or compressed (force wise)?
Energy is transferred to the elastic potential energy store
What forces need to be applied for an object to stretch, compress or bend?
More than one force acting on the object or otherwise it would just move in the direction the force is pushing/pulling
What is the relationship between extension and force applied/load?
They are directly proportional
What does the spring constant of a spring depend on?
The stiffer the material the greater the spring constant
What is the limit of proportionality of a spring?
When the force is great enough (limit to amount) that it is not directly proportional to the extension anymore
What is a moment?
The turning effect of a force
What can increase moment?
A larger force or a longer distance
What will happen if the total anticlockwise moment is equal to the total clockwise moment?
The object is balanced and won’t turn
What do levers do?
They increase the distance from the pivot at which the force is applied so less force is needed to get the same moment
What are gears?
Circular discs with teeth around the edges which interlock so that turning one causes another to turn
What are gears used for?
Transmit the rotational effect of a force from one place to another
How can gears be used to change the moment of a force?
The bigger the gear the bigger the moment as the distance from the pivot is greater
How do particles in fluids exert pressure?
Particles in fluids can flow and move around
They collide with surfaces and other particles
Particles are light but still have a mass and exert a force so they exert a pressure
What is the density of an object?
A measure of the compactness of a substance
How close together the particles in a substance are
How does density affect the pressure in a liquid?
The more dense a liquid is the more particles there are in certain space
This means more particles can collide so the pressure is higher
What happens to the pressure of a liquid as the depth increases?
The number of particles above that point increases
The weight of these particles adds to the pressure felt at that point
So liquid pressure increases
What happens to an object when they are in a fluid?
The pressure of the fluid exerts a force on it from all directions
Pressure increases with depth so the pressure on the bottom of the object is larger than on top
This causes a resultant force called up thrust
What is up thrust equal to?
Up thrust = weight of the fluid that has been displaced
What happens if the up thrust is equal to the weight of the object in a fluid?
The object will float
What happens if an objects weight is more than the up thrust in a fluid?
The object will sink
What happens if the object (in a fluid) is denser than the amount fluid it displaces?
It will sink
What happens to the atmospheric pressure as the altitude increases?
Atmospheric pressure decreases
Why does the atmospheric pressure decrease as altitude increases?
Because as altitude increases the atmosphere gets less dense so there are fewer air molecules that are able to collide with the surface
Also fewer air molecules above a surface so the weight of the air above is less
What is displacement?
A vector quantity
Distance with direction
If you walk 5m north and 5m south, what is your displacement?
0m
What does it mean when an object is travelling at a constant speed with a changing velocity?
The object is changing direction whilst staying at the same speed
What is the speed of a person walking?
1.5 m/s
What is the speed of a person running?
3 m/s
What is the speed of a person cycling?
6 m/s
What is the speed of a car?
25 m/s
What is the speed of a train?
30 m/s
What is the speed of a plane?
250 m/s
What is acceleration?
The change in velocity in a certain amount of time
What is the gradient on a velocity time graph?
Accleration
What is a flat section on a velocity time graph?
Constant speed
What is the area under a graph show for velocity time graphs?
The total distance travelled
What forces have to be balanced for an object to travel at a constant speed?
Frictional force and driving force
What is drag?
The resistance you get in a fluid (liquid or gas)
What does it mean if an object is streamlined?
It is designed so that fluid can flow easily across it therefore reducing the drag
What happens to an object when it falls?
The force of gravity is greater than the frictional forces so it accelerates
As speed increases friction builds up
The acceleration gradually decreases until the frictional force is equal to the accelerating force
This is its terminal velocity
What is Newton’s first law?
If the resultant force on a stationary object is 0 then it will remain stationary
If the resultant force on a moving object is 0 it’ll carrying on moving at the same velocity
What is the relationship between acceleration and mass?
They are inversely proportional
What will a non-zero resultant force produce?
Acceleration
What is Newton’s second law?
If a force acts on an object it will cause it to accelerate
What is Newton’s third law?
When two objects interact, the forces they exert on each other are equal and opposite
What is inertia?
The tendency to continue in the same state of motion
What is an objects inertial mass?
How difficult it is to change the velocity of the object
What can affect your thinking distance when braking?
Speed
Reaction time
What can affect your braking distance when braking?
Speed
Weather/road surface
Condition of tyres
How good your brakes are
What happens when you brake?
Brake pedal is pushed
Brake pads are pressed onto the wheels which causes friction which causes work to be done
Energy is transferred from the kinetic energy stores of the wheels to the thermal energy stores of the brakes (increases temp
How does speed affect braking?
The faster a vehicle is going, the more energy it has in its kinetic store, so more work has to be done to stop it
What factors affect momentum?
Increased velocity or mass means increased momentum
What is the momentum in a closed system?
Total momentum before = total momentum after (conservation of momentum)
