Forces Flashcards
What are 3 examples of contact forces?
normal contact force
tension force
friction force
What are 3 examples of non-contact forces?
Gravitational force
Electrostatic force
Magnetic force
What is the difference between vector and scalar?
Scalar quantities only have a magnitude and do not have a direction.
Vector quantities have both a magnitude and a direction.
If all the forces acting on an object balance out, then we say that the object is in:
Equilibrium
What are the 2 types of deformation of a spring?
elastic, inelastic
What does elastic deformation mean?
an object returns to its original shape after the forces have been removed
What is inelastic deformation?
an object does not return to its original shape after the forces have been removed
What is an object’s spring constant?
a measure of how many Newtons of force it would require to stretch (or compress) the object by 1 metre.
What are the units for spring constant?
N/m
What is Hooke’s law?
F = ke
force = spring constant * extension
What is an object’s elastic limit?
if you stretch an object past this limit it will start deforming inelastically
A _____ spring constant means the spring is more firm.
A _____ spring constant means the spring is less firm.
higher
lower
What is the formula for elastic potential energy?
energy = 0.5 * spring constant * extension^2
In a force - extension graph, The gradient of the straight part of the graph tells us the:
spring constant
In a force - extension graph, The area under the curve tells us the:
elastic potential energy
In a force - extension graph, The point where the line goes from straight to curved is referred to as the:
Elastic limit
or
Limit of proportionality
What is a moment?
the rotational or turning effect of a force.
What is the formula for moment?
Moment = force * (perpendicular) distance
What are the units for moment?
Nm
What is equation for weight?
weight = mass * gravitational field strength
What is the formula for pressure?
pressure = force/area
What are the units for pressure?
Pascals (Pa)
Which states of matter exert pressure?
all of them
What is the formula for acceleration?
acceleration = change in velocity / time
The gradient of a distance / time graph tells us:
speed
What does a flat line on a distance / time graph tell us about the movement of an object?
the object is stationary
What does a flat line on a velocity/time graph tell us about the object?
it is moving at a constant velocity
The gradient of a velocity / time graph tells us:
The acceleration or deceleration of the object
a straight diagonal line in a velocity/time graph shows us:
the object is accelerating
On a velocity / time graph, the distance travelled is shown by:
The area under the curve
What is the size of air resistance dependant on?
surface area and velocity
We say an object has reached ‘terminal velocity’ when it is falling with a _________ velocity.
constant
When is terminal velocity reached?
The weight has the same magnitude as the air resistance
The resultant force is zero
What is newton’s first law?
a resultant force is required to change the motion of an object
What is newton’s second law?
F = MA
the force is proportional to the objects acceleration
What is newton’s third law?
When two objects interact, the forces they exert on each other are Equal and opposite
What is the normal contact force?
the equal and opposite force exerted by an object when in contact with it and when it doesn’t move
A person weighs 800 N and is standing on the ground.
The ground is pushing upwards towards the person’s feet. How many newtons is this force?
800N
What is stopping distance?
the total distance a car travels from the moment when the driver first notices an obstruction, to when the car stops.
Stopping distance equals:
Thinking distance + braking distance
What are 3 things that may slow down a person’s reaction time?
being distracted
consuming alcohol
tiredness
What are 3 things that may increase braking distance?
Ice on the road
Worn tyre tread
Worn brakes
What is breaking distance?
the total distance a car travels from the moment when the breaks are first applied, to when the car stops.
if a vehicle drives twice as fast, what will happen to the breaking distance?
The breaking distance increases by four times
what is the relation between breaking distance and vehicle speed?
If the vehicle speed increases by a factor of 2, then the breaking distance will increase by a factor 2 squared (2^2), so 4 fold.
if increased by 3 it will increase by 3^2 (9) times
Which factor affects both the thinking distance and the braking distance?
Speed of the vehicle
What is the formula for momentum?
momentum = mass * velocity
What are the units for momentum?
kg m/s
The conservation of momentum principle states:
The total momentum before a collision is equal to the total momentum after the collision.
What formula relates force to momentum?
force = change in momentum / time
Which safety features of a car aim to slow the rate at which momentum is lost?
Crumple zones
Air bags
