P10 Flashcards
Force and motion (50 cards)
Describe three methods for a practical investigating Newton’s second law (the relationship between force applied and acceleration of an object, as well as the relationship between mass and the acceleration)
FORCE/ACCELERATION:
method 1
- gather equipment
[] chalk
[] metre rule
[] trolley
[] pulley
[] string
[] 10 10g masses
[] desk
[] phone
- on the desk, use the metre rule and chalk to draw markings along the long edge of the desk every 10cm
- attach a pulley to the end of the desk
- attach the trolley to a string and connect to the pulley
- FOR EACH MASS USED, TAKE 2 REPEAT MEASUREMENTS AND CALCULATE A MEAN FOR INCREASED ACCURACY
- place the 10 10g masses on the end of the string
[] hold the trolley at the start line on the desk
- have someone else use a phone camera to record when you let the trolley go (start recording as soon as let go)
[] if there are any zero errors in terms of the recording, account for these
- play back the video and record at which times in seconds the trolley passed each chalk line on the desk, pausing the video if you need to
- repeat with 80g to 20g
[] MUST PLACE MASS FROM PULLEY ON TROLLEY AFTER DONE; eg. at the end of the 100g, place two 10g masses on the trolley
[] this is because mass should be a control variable
- use (2xdistance(m))/time to get acceleration
- plot results (force on y-axis, acceleration on x-axis)
- should find that force and acceleration are proportional to one another
method 2
same thing as before but use light gates lol
MASS/ACCELERATION
same thing as method 1 but instead of changing force on pulley, keep force constant and continually add mass to the trolley
- should find that these two are inversely proportional
Give the equation for force (with units)
force (N) = mass (kg) x acceleration (m/s^2)
State Newton’s second law of motion
- an object’s mass is inversely proportional to its acceleration
- the resultant force on an object is directly proportional to its acceleration
What is inertia(l mass) (definition + equation for inertial mass) ?
- inertia is the tendency of a resting object to stay at rest, and an object in motion to stay in UNIFORM motion
inertial mass = force (N)/acceleration (m/s^2)
INERTIAL MASS IS A MEASURE OF THE DIFFICULTY TO CHANGE THE OBJECT’S VELOCITY
When is acceleration negative/positive ?
negative
- deceleration; resultant force (acceleration) is in the opposite direction to its velocity
positive
- acceleration; resultant force (acceleration is in the same direction as the object’s velocity)
What is the difference between weight and mass ?
- weight = the force acting on an object due to gravity
- mass = the quantity of matter in the object
How many newtons are in 1 kg ?
10N
Give the equation for weight (with units)
weight (N) = mass (kg) x gravitational field strength (N/kg)
Give the acceleration due to gravity on Earth
9.8 m/s^2
Give the gravitational field strength of Earth
9.8 N/kg
What measurement tool can measure weight ?
newton meter
Why do cars have a top speed ?
terminal velocity; the point at which the frictional force is equal and opposite to the driving force/weight
Explain terminal velocity using the example of a car
- at first, very little air resistance so the driving force is able to overcome air resistance
- as such the char accelerates
- as the car accelerates, air resistance on the car increases
- at a point, the car has a constant velocity and can no longer accelerate as the air resistance acting on the car is equal to the driving force, meaning the resultant force is 0
What is the frictional force on an object in a fluid ?
drag force
What does the braking force required to stop a vehicle’s movement depend on ?
- speed of vehicle at the time of applying brakes
- vehicle’s mass
What is stopping distance ?
- the shortest distance a vehicle can safely stop in
- stopping distance = thinking distance + braking distance
[] thinking distance is essentially the driver’s reaction time; how long it takes for them to actually realise the need to stop and then hit the brakes
[] braking distance is the distance travelled by the vehicle whilst the brakes are applied
Give the equation for final velocity squared using acceleration, initial velocity and distance
v^2 = u^2 + 2as
What equation should be used to calculate braking force ?
f = ma
Give some key factors affecting stopping distance
- tiredness
- alcohol
- certain drugs
- age
- high speed
- road conditions (ice/rain)
- worn brakes/tyres
- distractions to the driver
Give the equation for kinetic energy using mass and velocity
kinetic energy (J) = 1/2 x mass (kg) x velocity^2 (m/s)
Describe the energy transfers that take place when the brakes are applied to a car’s wheels and why they may have an adverse effect on the car in excess
- when brakes are applied, they press against the moving wheels, creating friction
- due to friction, kinetic energy from the wheels is transferred as thermal energy
[] as the car thus loses kinetic energy, it slows - if too much heating occurs, the breaks could overheat, wearing them down and making them less effective in future
Describe the relationship between a vehicle’s speed and both its stopping distance and the braking force needed to stop it
- higher speed = greater stopping distance
- higher speed = greater braking force needed
[] large braking force = possible overheating of brakes and possible loss of control of the vehicle
Calculate the braking force needed for a car of 1000kg that decreases in velocity from 30 m/s to 0 m/s in 10s
f = m x a
a = (u - v)/t
a = (30 - 0)/10
a = 3 m/s^2
f = 1000 x 3
f = 3000N
How much larger should the stopping distance be on wet roads and on icy roads ?
wet roads = x2
icy roads = x10
