physics topic 5 Flashcards
Scalars vs vectors
Scalars – only have size
Vectors – Size + direction
examples of scalars
time
mass
temperature
speed
examples of vectors
forces (including weight)
displacement
acceleration
velocity
how can vectors be represented
Vectors can be shown by arrows.
The length of the arrow shows the size,
or magnitude, of the force.
The direction of the arrow shows the
direction of the force.
The vector arrows can be added
together to show the resultant of
two of more vectors.
examples of contact forces
air resistance
friction
tension
normal force
examples of non contact forces
gravity
magnetism
electrical force
nuclear force
what is mass
Mass is the amount of matter in a
substance (Kg)
what is weight
Weight is the force (N) acting on an
object due to gravity
what is the gravitational field strength, g, on Earth
about 10 N/kg.
weight and mass are what
directly proportional
what is the centre of mass
The central point where mass is balanced from all sides
describe resultant forces
When both forces act in the SAME direction, the forces ADD up
When both forces act in the OPPOSITE direction, the forces SUBTRACT
describe hookes law of elastic behaviour
When an object is extended
after applying a force, it returns to its original shape and size once the force is removed
describe hookes law of inelastic behaviour
When an object is
extended after applying a force, it DOES NOT return to its original shape and size once the force is removed
describe the practical for finding the spring constant of a spring
Hang a spring from a clamp
Measure size of spring
Hang a weight on the bottom of the
spring
Measure the length
Measure the extension of the spring
Add further weights to the spring so the
force increases 2 N at a time up to 10 N
For each new force record the spring
extension
Use the formula F = k x e to calculate k
Sources of error
not clamping the ruler vertical
misjudging the position of the bottom of the spring – attach a pointer to the bottom of the spring
parallax error – make sure eye is level when measuring
what is the limit of proportionality when it comes to springs
Force and extension are proportional to
one another until a limit
After this point, the spring inelastically
deformes and will not return to its
normal length if the force is removed.
when an elastic band is streched what type of energy does it store
stores elastic potential energy.
describe the extension of an elastic band on a graph
The extension of an elastic band is not directly proportional to the force applied. A graph of extension against length for
an elastic band will produce a curve.
describe force extension graphs
The gradient of a force against
extension graph gives you the
spring constant of the spring.
how to find the elastic potential energy on a force extension graph
The energy stored as elastic
potential energy is the area under a force against extension graph.
detention of distance
How far an object has travelled. Distance is a scalar quantity.
what is displacement
How far an object has travelled in a straight line from the starting point to the finishing point and the direction of that line. Displacement is a
vector quantity.
what is speed
Speed is the rate of change of distance.
what is velocity
Velocity is the rate of change of distance.
what is the average walking speed
1.5 m/s
what is the average running speed
3 m/s
what is the average cycling speed
6 m/s
what is average speed
Average speed is the speed of an object over the entire journey.
what is Instantaneous speed
Instantaneous speed is the speed of an object at a given moment in time.
The speedometer in a car gives the instantaneous speed of the car.
what can distance time graphs be used for
Distance-time graphs can be
used to represent the motion
of an object.
how to find the instantaneous speed of the object at any point along the curve
tangent to the line must first be found – then the gradient of the tangent shows the speed.
what happens to an object when accelerating
When objects accelerate they can be changing speed or changing direction or changing both speed and direction.
what is acceleration
Acceleration is the rate of change of velocity, and since velocity is a vector so is acceleration.
why is direction important when thinking about acceleration
As acceleration is a vector the direction is important.
what is happening when a moving object has a negative acceleration
it can either be slowing down (often just called decelerating) or it could be increasing speed in the opposite direction.
velocity time graphs vs distance time graphs
A velocity-time graph gives more information than a distance-time graph.
As well as speed, distance travelled and time, a velocity-time graph will give
the acceleration of the object.
how do you find the acceleration off a velocity time graph
Found from the
gradient of the line
how do you find the distance travelled off a velocity time graph
The area
under the line on a velocity-time
graph is the distance travelled.
whats describe the forces acting on a skydiver when he reaches terminal velocity
The area under the line on a velocity-time
graph is the distance travelled.The area
under the line on a velocity-time
graph is the distance travelled.
what is newtons first law
if the resultant force on a stationary object is zero the object will remain stationary
if the resultant force on a moving object is zero it will just carry on moving at the same velocity
if there is a non zero resultant force on an object its velocity will change (it will accelerate in the direction of the force)
Non-zero resultant forces involve actions such as objects which are what
Starting
Stopping
Changing directions
Speeding up
Slowing down
what is newtons second law
The acceleration of an object is proportional to the
resultant force acting on the object, and inversely
proportional to the mass of the object.
In equation form, Newton’s Second Law is written as what
Force (N) = Mass (kg) x Acceleration (m/s2)
what is inertia
Inertia is a property of matter. It is the resistance of the object
to change its motion (speed and/or direction).
how is mass linked to inertia
Mass is a measure of the amount of inertia an object has. The
more inertia (or mass) an object has the harder it is to get
that object to change its motion.
what is newtons third law
Whenever two objects interact, the forces they exert on
each other are equal in size and opposite in direction.
give an example of newtons third law
When a car crashes into a crash barrier, the force acting on
the car and the force acting on the barrier are equal and
opposite.
what is thinking distance
Thinking distance is the distance that you travel while
reacting to a stimulus until you get your foot onto the brake pedal.
what is breaking distance
Braking distance is the distance you travel from pressing the
brake pedal until you come to a stop.
what is stopping distance
Stopping distance is the sum of thinking distance and
braking distance,
things that effect thinking distance (reaction time)
too much alcohol
poor visibility
tiredness
too many drugs
things that effect stopping distance
Icy roads
Tyres/brakes worn out
Wet roads
Driving too fast
what happens when work is done against
frictional forces on an abject
there is a temperature increase
of the object.
what type of quantity is momentum
vector
momentum is a conserved quantity what does this mean
The momentum of a system remains the same before and after an event.
e.g. In a car crash the momentum of the vehicles before
the crash equals the momentum of the vehicles after the
crash.
why are quick changes in momentum likely to hurt you
It’s the sudden coming to a stop.
why are there safety features in cars
to increase the time taken for the
momentum to change. By increasing the time taken, you
significantly lower the force being applied.
give some safety features of cars
crumple zones - part of the car designed to crumple on impact to increase the time it takes for the car to stop
seatbelts - stretch slightly increasing time for wearer to stop
airbags - inflate during collision so you hit the airbag not the dashboard slowing you down more gradually than if you had hit the dash board
