Mechanics Flashcards
What is a scalar?
A quantity with magnitude only
What is a vector?
A quantity with magnitude and direction
What are free-body diagrams?
Diagrams which show a single body on its own with the forces which act on the body, but not the forces the body exerts
How are forces resolved?
By splitting the force into horizontal and vertical components
When is a force board in equilibrium?
When the ring is at the centre
Define mass
The amount of matter in an object
Define weight
The force experienced by a mass due to a gravitational field
State the equation for weight
W = mg
What is a moment?
The turning effect of a force around a turning point
State the equation for moments
M(Nm) = F x d
State the principle of moments
For a body to be in equilibrium, the sum of the clockwise moments about a point must equal the some of the anticlockwise moments about the same point
What is a lever?
A rigid structure rotating around a pivot, in which an effort force works against the load force
What are couples?
- A pair of coplanar (act on the same plane) forces of equal size which act parallel to each other but in opposite directions
- This produces a turning effect
What is centre of mass?
The single point of an object that the whole weight can be considered to be concentrated
State the suvat equations
- v = u + at
- s = ut + 1/2at²
- s = (u+v/2)t
- v² = u² + 2as
- S = vt - 1/2at²
Define acceleration
The rate of change of an object’s velocity
Define displacement
How far an object’s travelled from it’s starting point
Define velocity
The rate of change of an object’s displacement
Define speed
How fast an object is moving, regardless of direction
How does increasing acceleration affect a displacement-time graph?
Gradient of the curve increases
What does the gradient of a displacement-time graph represent?
The velocity
What does the gradient of a velocity-time graph represent?
The acceleration
How is uniform acceleration displayed on a velocity-time graph?
Constant gradient
What does the area under the graph represent for a velocity-time graph?
The displacement
What does the area under the graph represent for a speed-time graph?
The distance travelled
What part of an acceleration-time graph is decelerating?
Below the x-axis
What does the area under an acceleration-time graph represent?
The total change in velocity
State newton’s first law of motion
An object will stay stationary or moving at a constant velocity unless acted upon by a resultant force
State newton’s second law of motion
F = ma, Force is directly proportional to the acceleration of the object
State newton’s third law of motion
- If two objects interact, they exert an equal and opposite force on each other
- Equal = Magnitude of force, Type of force
- Opposite = Direction of force
What is freefall?
The motion of an object undergoing an acceleration of g
State the freefall equations
- v = gt
- v² = 2gs
- s = 1/2gt²
- s = vt/2
What is projectile motion?
Motion with a constant horizontal velocity and a vertical velocity affected by acceleration due to gravity
What is drag?
Friction caused by a fluid
What is friction?
Force that opposes motion
What are the energy transfers that occur due to friction?
Kinetic energy is turned into thermal energy
What is lift?
An upward force on an object moving through a liquid
Define terminal velocity
The velocity at which the driving force match the frictional force
How is terminal velocity represented in a velocity-time graph?
The curve flattens at a certain velocity
How is terminal velocity represented in an acceleration-time graph?
The acceleration = 0
Describe the terminal velocity of a parachutist
- Leaves plane and accelerates due to gravity
- Accelerates until air resistance = weight
- Once close to ground, pulls parachute which increases air resistance
- Slows parachutist until air resistance = weight
- This terminal velocity is safe enough to land at
Describe the velocity-time graph of a parachutist
- Velocity increases until it reaches a terminal velocity
- Rapid drop in velocity until it reaches a new terminal velocity
Define linear momentum
The product of an object’s mass and velocity
State the units of linear momentum
Kgm/s
What is the principle of momentum?
Linear momentum is always conserved, assuming no external forces act
What is an elastic collision?
A collision where momentum and kinetic energy are conserved
Derive the equation for impulse
- F = ma and a = Δv/t
- F = Δ(mv)/t
- Ft = Δ(mv)
Define impulse
The product of force and time which is equal to the change in momentum of an object
Define work
The amount of energy transferred from one form to another when a force moves an object through a distance
State the work done equation
W = Fs where s is distance moved, in m
Define power
The rate of transfer of energy, in watts
What does the area under a force-displacement graph represent?
The total work done
State the equation of the power of a moving object with force acting at an angle
P = Fvcosθ
State the principle of conservation of energy
Energy cannot be created or destroyed. It can be transferred to different forms but the total energy in the system won’t change
Define kinetic energy
The energy of anything moving
Define potential energy
The energy gained by anything lifted
Derive the equation for efficiency of a motor
- E = mgΔh - useful energy output
- E = Pt = VIt = energy input
- Efficiency = mgΔh/VIt
What are the units for efficiency?
Efficiency has no units
What is mechanical energy?
The sum of the kinetic energy and potential energy in a system
What is mechanical energy?
The sum of the kinetic energy and potential energy in a system
What are the 3 characteristics of projectile motion?
- Vertical and horizontal motion are separate
- Motion is in a parabolic shape
- Acceleration is in one plane only
