Physics- Forces and motion Flashcards
Weight
W = mg
Acceleration
a = v - u/t
Force (acc)
F = Ma
[P2] Momentum
p = mv
[P2] Force (momentum)
F = mv - mu / T
Moment
Moment (Nm) = f x perpendicular d from pivot
Orbital speed
v = 2 PI r / T
Distance time graphs
Gradient = ?
Flat = ?
Curves = ?
Downhill means ?
Gradient = speed/steady speed
Flat = stopped moving
Curves = acceleration/deceleration
Downhill means going back towards starting point.
Velocity time graphs
Gradient = ? Flat = ? Uphill means? Downhill means? Area under graph? Curve?
Gradient = acceleration Flat = steady speed Uphill means acceleration Downhill means deceleration Area under graph is distance Curve means changing acceleration
Experiment to show average speed
Mass affects speed?
Friction affects speed?
Acceleration?
Toy car on a ramp:
- Mark a line on ramp so car starts at same point each time
- Measure distance between each light gate (3)
- Let go of car just before light gate
- Light gates connected to a pc- when car passes it breaks beam of light, time recorded by data loggers
- Repeat and get average time -> more reliable
- Find average speed
Load weights onto car
Lay different materials flat
Starting car at different places on ramp
Experiment on free fall
Sycamore seeds- small weight, large s.a.
- Collect a bunch, weigh them and measure wing length
- Use seeds with similar mass but diff wing lengths
- Drop seeds from same height
- Use stopwatch - how long to fall to ground
- Repeat - find average time
- Plot graph
First law of motion
Balanced forces mean no change in velocity
ZERO RESULTANT FORCE
Second law of motion
A resultant force means Acceleration
Unbalanced force = object accelerate in that direction
The bigger the force, acceleration?
Th bigger the mass, acceleration?
Bigger the force, greater the acceleration
Bigger the mass. Smaller the acceleration
[P2] Third law of motion
If object A exerts a force on object B, object B exerts the EXACT OPPOSITE force on object A
[P2] Vector quantities?
Scalar quantities ?
Examples of each
Vector - size and direction
Force, velocity, acceleration, momentum
Scalar - size
Mass, temperature, time, length
Stopping distance is
Thinking distance + braking distance
Thinking distance is…
Distance car travels in time between driver noticing hazards and applying brakes
Braking distance is…
Distance car travels during its deceleration whilst brakes are being applied
Thinking distance affected by…
How fast you’re going
How DOPEY you are - tiredness, drugs, alcohol, old age
Braking distance affected by…
How fast you’re going
Mass of vehicle - larger mass, longer takes to stop
Conditions of brakes
Grip - road surface, weather conditions, tyres
[P2] larger the force, ? Change of Momentum so a ? Acceleration
Larger the force, faster change of momentum, greater acceleration
[P2] how are cars designed to lessen injuries in a car crash? How?
CRUMPLE ZONES crumple on impact
Increasing time taken for car to stop
SEAT BELTS stretch slightly
Increasing time taken for wearer to stop- reduces forces acting on chest
AIR BAGS
Slow you down gradually
Longer it takes for change in momentum, smaller the force, less severe injuries
Larger force means ? Moment
Longer lever, ? Force, ? Moment. Why?
To get maximum moment… Why?
Larger force means larger moment
Longer lever means same force can exert a larger moment because distance from pivot is greater
To get maximum moment, push at right angles - perpendicular to lever because at any other angle means smaller moment as perpendicular d from pivot is smaller
How do you find centre of gravity of any shape?
- Suspend shape and plumb line for same point, wait until stops moving
- Draw a line along plumb line
- Do the same but suspend shape from different pivot point
- Centre of gravity is where two lines cross
What is the principle of moments?
If an object balanced,
Total a.clockwise moments = total clockwise moments
What is Hooke’s law
Extension is proportional to force
Experiment Hooke’s law
- Have a weighted stand, clamp, hanging masses, spring
- Measure length of spring when no mass on it
- Add one mass, measure length
- Repeat 6 times
- Repeat exp, calculate average length for each weight
What’s a galaxy
Large collection of stars
Geostationary satellites
Orbital period?
Used for?
Why?
Orbital period of One day
Communications
Always over same part of the planet
Comets
What are they
Orbits
Speed of orbits
Small lumps of icy rock
Very elliptical orbits around the sun
Travels much faster when near sun because GPE decreases, KE increases
