Mechanics Flashcards
what is a projectile
an object where the only force acting on it is its weight (assuming air resistance has no effect)
is air resistance is negligible what does this mean for forces on the object
there is no horizontal forces acting on the object so the horizontal velocity is constant throughout.
how do you calculate horizontal displacement
horizontal velocity multipled by time in the air
what is the vertical component in a projectile
as weight is the only thing affecting it the acceleration is due to gravity (9.81) gain every second
how can you calculate vertical values on a projectile
using SUVAT
how does air resistance change the trajectory of a projectile
the horizontal velocity slowly starts to decrease (as there’s air resistance), therefore not travel as far
vertical velocity will gain speed slower
what is friction
the force that opposes motion, turning kinetic energy into thermal energy and can never speed things up or start them moving
what are the 2 types of friction
contact friction-between 2 solid surfaces
fluid friction- called drag between liquids or gasses
what factors affect drag
increases when:
larger surface area
larger speed
larger density
what is lift
its an upwards force happening when moving through a fluid, causing the fluid its moving through to change direction
what directions do lift and drag act in
lift acts perpendicular to direction of fluid flow and drag acts parallel to it
what 3 things cause lift
if the wing diverts air downwards
impact of air on the wing (newtons 3rd law)
Bernoullis principle
what is Bernoullis principle
faster air means less pressure so air travelling over the top of the wing travels faster so more pressure is below the wing
what is terminal speed
when the frictional forces on an object equal the driving force on an object. there’s is no resultant force and now travels at a constant velocity
what is linear momentum
the product of an object’s mass and velocity
its a vector quantity
what’s the principle on conservation of momentum
the total momentum before the collision is equal to the total momentum after the collision provided there’s no external forces acting on the object
how does conservation of momentum effect explosions
the momentum before is 0, so it has to be 0 after the explosion. this is achieved by loads of fragments flying off in different directions
what is an elastic collision
where momentum is conserved as well as kinetic energy.
eg. collisions of air molecules
what is an inelastic collision
where momentum is conserved but kinetic energy isn’t conserved mostly lost through heat and sound
what is a perfectly inelastic collision
where the colliding objects stick together whether they are still moving or not. this is the maximum amount of kinetic energy that can be lost while still conserving momentum
eg. blue tac falling onto a table
what happens to the momentum of a single object in a collision
the momentum of the single object will change
what is change in momentum
force is equal to the rate of change of momentum
what is impulse
the product of force and time/ equal to change in momentum
how do you find impulse from a graph
the area under a force time graph
how do impulse and change in momentum have practical uses in cars
crumple zones-by increasing the impact time the force is smaller
airbags- prevent your head from hitting a hard surface and decelerating quickly
seatbelts
how do impulse and change in momentum have practical uses in sport
in sports like tennis and golf you want the ball to have the greatest velocity.
apply more force
use smaller mass
increase contact time
what is work
work is done when energy transforms from one form to another
what 2 things effect work done
the greater the force or the distance the object moved the more work needed to be done
how much work does a satellite do
none, the force of gravity is perpendicular to the force of motion so it cancels out
how can work be found on a graph
the area under a force against distance graph
what is power
the rate of doing work
what is the principle of conservation of energy
energy cannot be created or destroyed but can be transferred from one form to another. the total amount of energy in a closed system will not change
what is efficiency
a way of quantifying how much energy is being converted into useful energy, usually expressed as a percentage
when would you use SUVAT
when acceleration is uniform
what are key features of a displacement time graph
straight line gradient=velocity
curved line= acceleration (find tangents for velocity)
what do different gradients mean on a displacement time graph
steep gradient= high velocity
shallow gradient= low velocity
negative gradient= travelling backwards
horizontal gradient= stationary
how do you find average velocity on a displacement time graph
if the line is very curvy, draw a line of best fit and calculate the gradient from that
what are the key features of a velocity time graph
gradient= acceleration
area under graph= change in displacement
what do different gradients mean on a velocity time graph
steep= high acceleration
shallow= low acceleration
horizontal= constant velocity
negative= deceleration
what does a curved line mean on a velocity time graph
the curve means changing acceleration
what is the key feature on an acceleration time graph
area under the graph= change in velocity
above x-axis=positive change in velocity
below x-axis= negative change in velocity (slowing down)
what is newtons first law
if there is no resultant force acting on an object its either at rest or traveling at a constant velocity
what is newtons second law
F=ma
what is newtons third law
if object A exerts a force on object B, object B exerts and equal and opposite force on object A
what is meant by freefall
the object only has weight acting on it
why do all objects fall at g
with no air resistance all objects would accelerate at the same rate and therefore hit the ground at the same time
