TOPIC 2 FORCES AND MOTION Flashcards
how do you work out average speed
speed = distance/time
what are the units for average speed
metres/second
if an object travels at a constant speed what else stays the same
it is also travelling the same distance every second
why do we use average speed?
we use average as the speed may vary during the journey.
on a distance/time graph what does a steeper gradient represent
the object is travelling faster
on a distance/time graph what does a horizontal line mean
it means the object is stationary
on a distance/time graph what does a curved line represent
it means the speed of the object is increasing (changing)
how do you work out speed from a distance time graph
speed=gradient- yaxis/xaxis
is speed scalar or a vector quantity
speed is a scalar quantity
what is a scalar quantity?
something that only measures magnitude e.g speed
what is a vector quantity?
something that measure both magnitude and direction
is velocity a speed or a vector quantity
vector
what is the equation for acceleration using velocity and time
acceleration = change in velocity/ time taken
what is does the gradient of a velocity time graph represent
acceleration
what does the area under a velocity time graph represent ?
the distance travelled
how can you use an experiment to investigate the motion of objects (toy car or tennis ball…)
the light gate experiment
how do you set up a light gate experiment
set up a ramp of about 15degrees
measure out the length of the object(a card)
set up a single light gate at the bottom of the track and connect to a data logger and get it to record speed.
allow the trolley to run down the ramp
measure the distance travelled by the trolley release point and the light gate
use a stop watch to measure how long the trolley takes to travel between these two points
record speed from the data logger
how does a light gate calculate speed
the light gate starts a timer - it measures how long the beam of light is broken for and if we know the length of the card (in metres) we can calculate speed.
what are the errors with the light gate experiment
The reaction time from the stop watch and the judgement of when it goes through the beam
The experiment uses speed = distance/time however the trolley accelerates
There could be human error in measuring distance and error in releasing the trolley
what does a horizontal line on a velocity time graph?
the object is travelling at a constant speed
what are the units for any force
newtons (N)
what is a force ?
a force is a push or a pull - it can change shape, speed and direction of the object
name some examples of forces
Gravity, Electrostatic, Thrust, Drag, Lift, Tension, Magnetic, Friction.
is force a vector or scalar quantity
vector
what is the equation for force
f = mass x acceleration
what is the equation for weight
weight = mass (kg) x acceleration (due to gravity)
what are the units for weight?
N/kg
what is the difference between weight and mass
weight is a force and depends of the strength of gravity whereas mass is the amount of matter and does not change
what are the units for acceleration
m/s2
what is newtons 1st law?
Objects will stay stationary or continue to move with a constant speed, unless an unbalanced force acts upon them
what is newtons 2nd law?
The acceleration produced by a force when it acts on a body is proportional to the force and takes place in the same direction as the force
what is newtons 3rd law?
To every force there is an equal and opposite reaction force
describe the forces acting on a falling object and why they reach terminal velocity
Initially the only force acting is weight so there is a resultant force downwards and therefore it will accelerate. The speed will increase and therefore drag will increase resulting in the resultant force to decrease. Eventually weight will equal drag which means that the resultant force will equal 0 meaning the object has reached terminal velocity.
in a falling skydiver, what forces are acting
weight is pulling him towards the floor and resistance (drag) is acting against the skydiver upwards
how does shape and area affect a falling object
Drag depends on shape and area.
For example; a skydiver
Without a parachute open they have a small area and a force equal to the weight- but with a parachute they have a much larger area. There is a much larger force of drag or air resistance acting on the body and in comparison a smaller weight force pulling them down so this means terminal velocity will lower.
describe friction
friction is a force which opposes motion. Friction occurs in many ways on objects - with static motion on solid gripping surfaces, sliding friction when solid surfaces move past each other or resistance in liquids and gases (more drag on an object the slower it can move) - friction always increases when the speed of the object increases
Name the safety features of a car
Crumple zones
Seat belt
Air bag
How do crumple zones reduce the impact forces on passengers
They absorb the kinetic energy of the crash , work = force x distance - a large stopping distance reduces the stopping force Force= mass x acceleration increasing stopping time and reduces deceleration and therefore also reducing the force
How do seat belts reduce impact forces on passengers
According to newtons first law “an object will stay stationary or move at a constant velocity unless acted on by an unbalanced force”. The flexible material increases stopping distance, this reduces acceleration (F=ma) and (F=mv/t) and makes stopping distance smaller. It prevents contact with the steering wheel and windscreen. Also the seatbelt covers the sturdy parts of your body e.g. pelvis and chest meaning there is a large surface area covered and reduces pressure
