Mechanics Flashcards
(20 cards)
What is Newton’s first law of motion?
Objects at equilibrium will not accelerate:
A body at rest will remain at rest
A body that is in motion, moving with a given velocity, will continue moving at that velocity
UNLESS a resultant external force acts on it.
What is Newton’s second law of motion?
F=ma
The acceleration of an object is:
Directly proportional to the resultant force acting on it
Inversely proportional to its mass
What is Newtons’s third law of motion?
For every action, there is an equal and opposite reaction
When objects interact, they exert equal and opposite forces onto each other
As forces occur in pairs, one object cannot exert a force on another object without experiencing a force itself (of equal magnitude and opposite direction)
What is the equation for momentum?
p=mv
momentum (kgms-1) = mass (kg) x velocity (ms-1)
What is the principle of conservation of linear momentum?
The total momentum before an event/collision = The total momentum after an event/collision
(in a closed system)
∑ pBEFORE = ∑ pAFTER
m1v1 = m2v2
What is terminal velocity?
The maximum velocity and object can reach when falling through a fluid
Occurs when the drag forces acting on the object = the weight of the object
As it has no resultant force, an object moving at terminal velocity has no acceleration
What is a moment?
The turning effect of a force
Moments cause objects to rotate about a point or axis
What is the equation used to calculate the moment of a force?
M = F𝒳
moment (Nm) = Force (N) x Perpendicular distance between the line of action of the force and the axis of rotation (m)
What is the principle of moments?
For a system to be in equilibrium:
The sum of the clockwise moments about a point = The sum of the anticlockwise moments about the same point
What are kinematic equations?
State the four you are required to know
A set of equations which can describe any object moving with a uniform acceleration
v = u + at
s = ut + ½at2
v 2 = u2 + 2as
s = (u + v)t/2
What are scalar and vector quantities?
Provide examples for each
Scalar quantities: quantities that have a magnitude
e.g. speed, distance, time, mass, energy, temperature, etc
Vector quantities: quantities that have both a magnitude and direction
e.g. velocity, acceleration, displacement, momentum, etc
What is the centre of mass/gravity of an object?
The single point through which the object’s entire weight can be said to act
For symmetrical objects, with a uniform density, the centre of mass is located at the point of symmetry
What is the conservation of energy?
Energy cannot be created or destroyed in a closed system, only transferred from one energy store to another
What are the equations for efficiency?
efficiency = useful energy output/total energy input
or
efficiency = useful power output/total power input
What are the equations for kinetic energy and gravitational potential energy?
Kinetic Energy:
Ek = ½mv2
Gravitational Potential Energy:
ΔEp = mgΔh
What is the equation for weight?
W = mg
What is the definition and unit of power and its corresponding equations?
Power is the rate of change of energy transfer, measured in Watts (W)
∴ P = E/t = ΔW/t = FΔs/t
What is free fall?
The motion of an object under the influence of gravity alone, with no other forces acting on it
What is work done?
The amount of energy transferred when a force causes an object to move over a certain distance
What is the equation for work done?
ΔW = FΔs
Work done (J) = Force parallel to/applied in the direction of motion (N) x displacement (m)
