2. Mechanics Flashcards
What are the equations of motion / suvat equations?
s=((u+v)/2)t
s=ut+1/2at^2
v=u+at
v^2=u^2+2as
What is suvat?
We use suvat when an object is moving at uniform acceleration
s=displacement(m)
u=initial velocity(ms^-1)
v=final velocity(ms^-1)
a=acceleration(ms^-2)
t=time(s)
What is instantaneous velocity?
The velocity of an object in a specific point in time (instantaneous)
How does an acceleration time graph work?
Represent the change in velocity overtime
area under graph = change in velocity
What is uniform acceleration?
where acceleration is constant
What’s the difference between scalar and vector?
Scalar gives 1 piece of info
no direction, just magnitude
E.g distance, speed, mass
Vector gives 2 pieces of info
has a direction and magnitude
E.g displacement, velocity, weight
What is resolving a vector?
splitting it into it’s horizontal and vertical components
What does it mean when an object is described as uniform?
It’s centre of gravity is exactly at the centre
So its weight is counted from exactly the centre
What’s Newton’s 1st Law?
A body will remain at rest or constant v if no force is being acted on it
Needs a resultant force on object to move
What’s Newton’s 2nd Law?
The acceleration of a body is proportional to the resultant force
So acceleration is in the same direction as the force
f=ma
What’s Newton’s 3rd Law?
When body A exerts a force on body B, body B exerts an equal opposite force on body A
It must be a reaction between the 2 bodies
This has to happen as they are in equilibrium
Has to be same type of force
E.g the table exerts an equal and opposite force on the mac
What are moments?
A moment is a ‘turning force’
Moment(Nm)=force(N) x perpendicular distance from pivot(m)
M=Fxd
This makes moments acting clockwise and anticlockwise
What’s the principle of moments in angles?
Σ clockwise moments = Σ anticlockwise moments
for equilibrium
What happens when there’s several moments?
If in equilibrium, and there’s 1 clockwise and 2 anticlockwise moments:
M(1)=M(2)+M(3)
w(1)d(1)=w(2)d(2)+w(3)d(3)
What is the conservation of energy?
Energy can never be lost or gained out of nowhere
- only through transfers
What is Kinetic energy?
Ek is the energy an object has due to it’s motion
Ek=1/2 x mv^2
What is gravitational potential energy (GPE)?
GPE is the energy an object has due to it’s height above the ground
GPE=mass x gravitational strength x height
Ep=mgh
What happens with GPE and Ek in an elastic reaction?
GPE at top = Ek at bottom
mgh=1/2 xmv^2
Why doesn’t a ball bounce all the way back up?
The ball is working against resistive forces
So some Ek is given to the environment in the form of heat due to air resistance
What is work done?
Work done (J) is simply the force needed to move an object by a certain distance
W=F△s
where s=displacement
What is power?
Power (Watts) is the rate of doing work
P=△W/△t
What power equations can be derived?
P=△W/ △t
So P=F△s/△t
So…
P=Fv
where v=velocity
What is momentum?
Any object with a mass and velocity has a momentum (p)
Momentum(kgms^-1)=Mass(kg) x velocity(ms^-1)
P=mv
What’s the principle of momentum?
Momentum is always conserved in any interaction where no external forces act
- So momentum before = momentum after
What is projectile motion?
The motion when an object is thrown into the air, so it has gravity’s acceleration and force acting upon it
projectile motion curves as gravity finally takes it over
How do x and y move in projectile motion?
x and y are independent from each other
- so it doesn’t matter how far x travels, 0 or 100, y will still move at the same pace as if x wasn’t there
The object hits the bottom when y hits the bottom
The horizontal velocity is always a constant
- only the vertical velocity changes
How must we answer questions asking for the velocity at an angle?
Must give the magnitude and direction
- Direction as an angle
- E.g 53.13 deg to horizontal
