Mechanics Flashcards
Define velocity
The rate of change of displacement. v = s/t
Define acceleration
The rate of change of velocity. a = (v-u)/t
What is a moment
The turning effect of a force. Moment = force x perpendicular distance from the pivot to the force.
Define the principle of moments
For an object to be in rotational equilibrium, the sum of the anticlockwise moments is equal to the sum of the clockwise moments about the same point.
Define the centre of gravity
The point at which all weight of a body appears to act
Define Newton’s First Law
An object will remain at rest or at constant velocity unless a resultant force acts upon it.
Define Newton’s Second Law
Force = mass x acceleration. If the acceleration is 0ms^’2 then Force is 0N.
Define Newton’s Third Law
Every action has an equal and opposite reaction. Forces always come in pairs.
Define momentum
Momentum is a measure of an objects motion. Momentum = mass x velocity. p=mv. kgms^-2
What are the SUVAT equations?
v^2 = u^2 + 2as s = ut +1/2at^2 v = u + at s = 1/2(u+v)t
Define projectile
The motion of anything launched into the air and the forces acting on it are air resistance and gravity.
How would you determine the horizontal and vertical velocities?
Vertical: Acceleration is constant, therefore SUVAT
Horizontal: No horizontal force (acceleration), therefore v = s/t
Define an elastic collision
Kinetic energy is conserved.
Define an inelastic collision
KE is not conserved. Lost energy will have been transferred to heat and sound energy.
Derive an equation for particle momentum
E=1/2mv^2 p=vm
E=1/2m(p/m)^2
E=p^2/2m
Define impulse and state the equation.
The change in momentum.
Impulse (Ns) = Force(N) x time (s)
Define angular velocity
The rate at which angular displacement changes. Unit - radians per second.
Define angular displacement
the vector measurement of the angle through which something has moved.
Angular Velocity equations
ω=θ/T
v = ωr
T = 2π/ω
Define centripetal acceleration
the acceleration towards the centre of a circle corresponds to the changes in direction to maintain motion around circle
Centripetal acceleration
a= rω^2
Define centripetal force
The resultant force towards the centre of the circle to maintain an objects circular motion
centripetal force
F = mrω^2 =mv^2/r
Centripetal force needed will be larger if:
- rotating object has more mass.
- objects rotate faster.
- object is further away from the centre of circle.
Explain why a body moving at constant speed in a circular path needs a resultant force
acting on it.
The direction of speed/velocity is changing. There is an acceleration/rate of change in momentum
Define power
Rate of energy transfer. P=E/t
Equation for work done
W=Fd
A projectile would have a greater range on the Moon than the Earth because of the
lower gravitational field strength and because of the lack of an atmosphere. Explain how each of these factors would increase the range of the projectile.
Smaller acceleration, causing longer time of flight. No work done against friction, as there is a lack of atmosphere.
Explain why pulling the trolley a certain distance requires the person to do less work than pushing the trolley the same distance
Pulling trolley gives upwards force on the trolley, so there is less normal contact force. Friction is less. Less force is required to from the person. W=Fd, so less work done.
