Section 4.1 - Mechanics Flashcards
Define vector
A quantity with both magnitude and direction
Define scalar
A quantitiy that has no direction
What are 5 examples of a Scalar?
Distance,Density, Temperature,Energy,Speed
What are 5 examples of a vector quantity?
Force,Displacement,Acceleration,Velocity,
Momentum
Define displacment
Distance in a given direction
Define Velocity
- Speed in a given direction
- rate of change of displacement
Define acceleration
Rate of change of velocity
What is it called when the resultant of all the forces on an object equals 0?
Equillibrium
Define a moment
The force * perpendicular distance from the line of action of the force to the pivot point
What is the principle of moments?
The sum of the clockwise moments is equal to the sum of the anti-clockwise moments
Define centre of mass
The point through which a single force on the body has no turning effect.
What is the moment of a couple?
Moment of a couple = Force * Perpendicular distance between the lines of action of forces
What must be true for two forces to be considered a couple?
- Acting around a pivot
- Equal and opposite forces but not along the same line
What is stable equilibrium?
If a body in stable equillibrium is displaced then released it will return to its equilibrium position
What is unstable equilibrium?
When a body in unstable equilibrium is displaced it will not return to its equilibrium postion
What is the gradient of a displacement/ time graph?
Velocity
What does a x vs t graph look like at consant velocity
Linear
What is the gradient of a velocity / time graph
Acceleration
What is the formula for constant acceleration
a = v - u
—–
t
What are the SUVAT equations?
V = u +at
S = ut + 0.5 *at²
S = vt - 0.5 *at²
V² = u² + 2as
S= 0.5(u+v)t
What is the area under a V/t graph
Displacement
What is the area under an a/t graph?
velocity
Define free fall
An object that is accelerating due to gravity
What is terminal velocity?
Terminal speed occurs where the frictional forces acting on an object and driving forces are equal, therefore there is no resultant force and so no acceleration so the object travels at a constant speed
How does air resistance affect projectile motion?
Greatest hieght and distance are both reduced
What is newtons 1st law?
An object will remain at rest or constant velocity unless acted upon by an external force
What is newtons 2nd law?
The acceleration of an object is proportional to the resultant force experienced by the object
What is newtons 3rd law?
Every action has an equal and opposite action that is :
* equal in magnitude
* the same type of force
* in the opposite direction
* acting on a diffent object
What is a free body diagram?
a diagram which shows all the forces that act on an object
What is stopping distance?
Thinking distance + braking distance
What is braking distance?
The distance travelled by a car from the moment the brakes are applied
What is thinking distance?
The distance travelled in the time it takes the driver to react
What is momentum?
p = mass * velocity
What is the unit for momentum?
kgm(s^-1)
Extended version of newtons second law?
Force is proportoinal to the rate of change of momentum
What is impulse?
Ft = Δ(mv)
What is the area under a force time graph?
The impulse
What is the change of momemntum when an object rebounds normally?
-2mu
What is the change of momentum when an object does not rebound normally?
-2mu.cosθ
What is the principle of conservation of momentum?
total momentum remains constant provided no external reultant force acts on the system
What is the equation for the force on object A in terms of mass and velocities?
F = (mₐuₐ - mₐvₐ)/t
What is the equation for the forces on two objects colliding?
Fₐ = -Fᵦ
What is the eqaution for total final momentum?
mₐvₐ+mᵦvᵦ =mₐuₐ + mᵦuᵦ
What is the velocity of the two objetcts if they stick together?
They have the same velocity
What is an elastic collison?
- A collision in which there is no loss of kinetic energy.
- Energy and momentum is conserved
What is an inelastic collision?
- The colliding objects have less kinetic energy after the collision than before
- Only momentum is conserved
Is an explosion an elastic or inelastic collision?
inelastic
List 4 stores of energy
- GPE
- Kinetic
- thermal
- Elastic
List 3 ways of tranfering energy
- Radiaiton
- Electrically
- mechanically
What is a joule?
The energy needed to raise 1N through a vertical height of 1m
What is the principle of conservation of energy?
Energy cannot be created or destroyed
What is work done?
- W = force * distance moved in the direction of the force
- W = F.s.Cosθ
What is the area under a F vs d graph
Work done
What is kinetic energy?
The energy due to an objects motion
Formula for kinetic energy?
Ek = 0.5*mv²
What is potential energy?
The energy due to an objects positon
What is the formula for GPE
GPE = mgΔh
What is power?
The rate of transfer of energy
What is the formula for power in terms of force?
P = fv
Formula for efficency?
e = useful energy out
======
total energy in
Describe and Explain
Uniformly accelerated motion
- Constant acceleration
- Resultant force = m.a where m is constant
- SUVAT
- Each dimension has separate equations
- S vs t graph is a quadratic graph; S = ut + 0.5at²
- v vs t graph is a linear graph; gradient is a
- a vs t graph horizontal line
Describe and Explain
Newtons second law of motion
- RF = ma; Resultant force is the product of mass and acceleration
- RF = (mv - mu)/t = ΔP/t
- Force is proportional to the rate of change of momentum
Describe and Explain
Projectile motion
- Parabolic trajectory
- sᵪ = uᵪ * t
- sᵧ = uᵧt + 0.5* gt²
- vᵧ = uᵧ + at
- vᵪ = uᵪ
- aᵪ = 0; constant horizontal velocity
- aᵧ = g = -9.81; constant vertical acceleration
Describe and explain
Hookes’ law
- Force applied by a spring is in the opposite direction to the extension
F = k.e
E = 0.5 * Fe = 0.5ke²
Describe and explain
Newtons 3rd law of motion
- Forces occur in pairs
- Equal in magnitude
- Same type of Force
- oppostie in direction
- act on different objects
Describe and explain
Conservation of Linear momentum
- P =mv
- Sum of momentum before = sum of momentum after
- momentum is conserved in a particular direction
- No external forces act on the system
- F₁ = (m₁v₁ - m₁u₁)/t 2nd law
F₂ = (m₂v₂ - m₂u₂)/t 2nd law
F₁ = -F₂
