Motion Flashcards
what is the instantaneous velocity
the velocity at a given instant in time
what is the average velocity
the total displacement divided by the total time taken
how to find the instantaneous velocity from a curved displacement-time graph
draw a tangent to the point then find its gradient
whats the velocity of an object bouncing at the very top
0m/s
whats the acceleration of a bouncing object
g (-9.81m/s^2)
experiment to determin g
- set up a steel ball and trapdoor
- record ball height
- open door and time how long it takes to drop (can use pressure plate and electronic timer)
- record average of three attempts
- measure time form a range of heights
- plot a graph of hight against time^2 (should be straight)
- calculate g (its the gradient * 2)
what is lift
it’s the upward force caused by collisions with air particles on the underside of a wing
how does a plane create lift
as it moves forward it pushes air particles down. this causes an equal and opposite upward force on the wings
how are wings shaped and why
angled top maximise the amount of air it can push down.
curved and smooth to reduce drag
what is friction
the resistance to motion due to contact forces
what does friction do
it converts kinetic energy into other types (mostly thermal)
what is drag
it’s a frictional force caused by motion in liquids and gases caused by collisions with particles.
factors affecting drag
speed of an object
the shape of the object (how streamlined it is)
surface area
what is air resistance
the frictional force (drag) opposing the motion of an object travelling through air
how is terminal velocity reached
weight stays constant so the downward force doesn’t change. as the objects speed increases the drag increases until it equals the weight. when this occurs the object is at terminal velocity
why do parachutes slow your fall
the increased surface area increases air resistance. the resistive force is now greater than the wight. this causes deceleration. the speed decreases and so does the drag until its equal to the weight again. this is at a new slower terminal velocity
factors affecting reaction time
drugs/alcohol
fatigue
distractions
how does the velocity of a vehicle change the stopping distance
the thinking distance increase linearly with the velocity and the braking distance is proportional to the velocity^2
an important thing about projectile motion?
the horizontal and vertical components are independent meaning they are solved separately
what forces act on projectiles
only gravity. the vertical acceleration is always 9.81m/s^2 and the horizontal is always 0
What’s Newton’s first law
the velocity of an object won’t change unless a resultant force acts upon it
What’s Newton’s second law
force and acceleration are directly proportional
What’s Newton’s third law
when a force acts on an object it applies an equal and opposite force back (for every action there is an equal and opposite reaction)
what is the impulse of an object?
its change in momentum
what is the conservation of momentum?
momentum can not be created or destroyed so momentum before a collision = momentum after a collision
difference between elastic and inelastic collisions
elastic collisions conserve kinetic energy and momentum. inelastic collisions only conserve momentum because some energy is dissipated as thermal or other energy
what type of collision is an explosion
its a reverse collision. it is an inelastic process as kinetic energy is not conserved. the kinetic energy comes from the internal energy
what are some safety features in cars?
airbags
crumple zones
seat belts
how do safety features of a car work
they absorb some of the kinetic energy from a collision. they increase the time taken for the change in momentum to happen, reducing the force
definition of a radian
the angle between two radii of a circle that are connected with an arc equal to the radii’s length
what is the angular speed
a measure of how quickly an object’s rotating. the change in angle divided by the change in time
whats the period in circular motion
the amount of time taken for one resolution
whats the frequency in circular motion
the number of times it goes around the circle per second
why is an object in circular motion always accelerating
acceleration is the change in direction or magnitude of velocity. in a circle, the direction is always changing so an object is always accelerating and its always towards the centre of the circle
why is the acceleration of circular motion towards the centre
the change in velocity is always towards the centre. this is called centripetal acceleration
what is centripetal force
any force that causes circular motion. the larger the force the smaller the circle. it’s always perpendicular to instantaneous velocity
define simple harmonic motion
any motion where the acceleration is directed towards a fixed point and is directly proportional to the negative of the displacement
whats the gradient of an acceleration-displacement graph
the angular frequency (notation- ω) squared by -1. to get the angular frequency square root the
(gradient * -1)
gradient = -1(ω^2)
for simple harmonic motion how do acceleration-time graphs and displacement-time graphs differ
they are a reflection in the X-axis of each other.
how does the GPE, KE and EPE change in a pendulum simple harmonic system
at the centre of the oscillation, KE is at a maximum and GPE and EPE are at a minimum. at the top of the oscillation, the GPE and EPE are at a maximum and KE is 0.
what is a damping force
and force opposing motion (frictional forces)
what happens when an oscillation is damped
the amplitude decreases. the period and frequency remain the same
what are under-damping and over-damping
under-damping is when the effects of damping are so minor it would take a long time to see a decrease in amplitude
over-damping causes no oscillations. the object just returns to equilibrium slowly. when the object returns to equilibrium as quickly as possible this is critical-damping
how can you find a resonance curve
plotting a graph of amplitude against frequency
how does damping affect the resonance curve
the greater the damping effect is the flatter the resonance curve is
when does resonance occur
when the applied frequency and natural frequency are similar
