Mechanics Flashcards
What property does a scalar quantity have?
Magnitude only.
What properties do vectors have?
Both magnitude and direction.
Examples of vector quantities:
Velocity, displacement, acceleration, forces, momentum, weight, moments.
Examples of scalar quantities:
Speed, distance, electrical power, charge, mass, energy, current, potential difference.
Speed is…
…rate of change of distance.
Velocity is…
…rate of change of displacement.
Acceleration is…
…rate of change of velocity.
Equation for acceleration using velocities:
a=Δv/Δt
What is unit acceleration measured in?
ms^-2
The gradient of a velocity time graph represents what?
Acceleration.
The area under a velocity time graph represents what?
Displacement.
Define a moment.
The turning effect of a force at a distance perpendicular to the force.
Equation for moments:
M = Fd
Where:
M is the moment.
F is the force.
d is the distance perpendicular to the force from the pivot.
Moments are measured in what?
Nm.
Centre of mass is what?
The mean position of the mass of an object.
Centre of gravity is what?
The position at which weight acts if the object is considered as a single position; the point at which there is no moment due to weight.
In a uniform gravitational field, what can be said about the centre of mass and the centre of gravity?
They are in exactly the same place.
An object is stable, when?
If the line of action from the centre of gravity lies within the base of the object.
How can an object be made more stable?
An object can be made more stable by lowering the centre of gravity or by widening the base.
What is the principle of moments?
A system can be said to be in equilibrium if the sum of the total anticlockwise moments equals the sum of the total clockwise moments.
What equipment can be used to find the centre of gravity of an object?
A clampstand.
A plumbline.
A nail.
Equation for kinetic energy:
Ek = 1/2 mv^2
Equation for gravitational potential energy:
ΔEp = mgΔh
Elastic potential energy equations:
Eel = 1/2 Fx
or
Eel = 1/2 kx^2
Equation for work done:
W = Fscosϴ
What can a vector be resolved into?
A horizontal component and a vertical component.
How do we resolve to find horizontal and vertical components of vectors?
Use trigonometry.
Sine to find the vertical component.
Cosine to find the horizontal component.
What does SUVAT stand for?
S for displacement/m. U for initial velocity/ms^-1 V for final velocity/ms^-1 A for acceleration/ms^-2 T for time/s
What are the four equations of motion?
v=u+at
s=ut+1/2at^2
v^2=u^2+2as
s=1/2(u+v)t
When can the equations of motion be used?
If acceleration is constant!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
How do we calculate the motion of projectiles?
Resolve the given vector into vertical and horizontal components and write out the suvat for each. Work from there to solve the problem.
How do you solve parabola problems?
Resolve the vector into vertical and horizontal components then write suvat for each on the first half of the parabola. Don’t forget to do the same to the second half of the parabola because if something goes up it also comes down.
State Newton’s 1st Law of Motion.
An object will continue to move with a uniform velocity unless it is acted on by a resultant external force.
State Newton’s 2nd Law of Motion.
F=ma
Force in Newtons (N).
Mass in kilograms (kg).
Acceleration in metres per second squared (ms^-2).
State Newton’s 3rd Law of Motion.
Every action has an equal and opposite reaction. (If object A exerts a force on a second object, B, then B exerts an equal, but opposite, force back on object A).
A magnet exerts a magnetic force on a lump of iron. What is the Newton’s 3rd Law pair of these forces?
The iron exerts a magnetic force on the magnet.
What is the Principle of Conservation of Momentum.
The Principle of Conservation of Momentum states that in a closed system momentum is conserved.
What is a closed system?
A system where there are no external forces acting.
Equation of momentum.
p=mv
Momentum in kgms^-1
Mass in kg
Velocity in ms^1
Is momentum a vector or a scalar?
Vector quantity.
Resultant force of an object can be described as rate of change of what (Newton’s 2nd)?
Momentum.
Recoil is a result of what?
The Principle of Conservation of Momentum. If objects didn’t recoil then momentum would not be conserved.
Static objects are objects that can be said to be in what?
Equilibrium.
An object in equilibrium has what resultant force?
0 Newtons.
Static objects can be either what or what?
Stationary or have constant velocity (Newton’s 1st Law).
First step for calculating forces for statics is…
…ΣF=0
If the static is on a slope the angle between the slope and the horizontal is the same as what?
The angle at the top of the resolved vector.
Dynamics are what?
Situations involving resultant forces and accelerations.
First step for dynamics questions…
…ΣF=ma
