Topic A - Mechanics

Define a scalar quantity & give examples

Quantity that has only magnitude(size)

Examples: Distance, Energy, Speed, Mass, Power, Temperature

Define a vector quantity & give examples

Quantity with a magnitude (size) and a spatial direction.

Examples: Displacement, Acceleration, Velocity, Momentum, Force

How do you add vectors algebraically

1. Resolve all vectors in horizontal and vertical components.

2. Sum the vertical components and horizontal components individually.

3. Use Pythagoras theorem to solve for the resultant vector.

4. Use TOA to find the angle.

List SUVAT

S - displacement/distance - m 

U - initial speed/velocity - ms^-1

V - final speed/velocity - ms^-1

A - acceleration - ms^-2

T - time - s

Distance

How far in total an object has travelled

Displacement

How far an object has travelled from the start to finish in a straight line (with direction).

Speed

Total distance travelled per unit second

Velocity

Rate of change of displacement

Acceleration

Rate of change of velocity

What is the gradient on a displacement time graph?

The velocity

How do you measure the instantaneous velocity on a displacement time graph? 

Take the gradient of the tangent line of the point you are measuring.

What is the gradient on a velocity time graph?

The acceleration

What is the area under on a velocity time graph?

The displacement

What is the area under on a acceleration time graph?

The change in velocity

List the 5 SUVAT equations.

s = (u + v / 2)*t

v = u + at

s = ut + ½ at²

v² = u² + 2as

s = vt - 1/2at²

Define Projectile Motion

The motion of an object thrown into the air.

What is the only force that will be acting on a object after the initial force and if air resistance is negligible ?

Weight Force - 9.8ms^-2

What is the principle when air resistance isn’t negligible?

It is proportional to the square of the velocity.

• F = ½ ρAv²

State the air resistance formula

F = ½ ρ A v²

How does the path a projectile takes change when Air resistance is increased? (List 3 things)

• It reaches a lower vertical height

• It travels less far horizontally

• The path become asymmetrical with the section before the peak as it is longer than the section afterwards

What are the 4 main ways energy can be transferred?

Mechanically - an object moving due to a force acting on it

Electrically - a charge moving through a p.d

Heating - energy transferred from a hotter object to a colder object

Radiation - energy transferred by e.g. light/sound

Work

Amount of energy transferred from one stores to another.

State the mechanical work formula

W = Fscosθ

What is the difference if work done is negative or positive?

If the work done is positive then work has been done on the object, if it is negative then work has been done by the object.

What is the formula for GPE?

ΔE_p = mgΔh

What is the formula for EPE?

ΔE_H = ½ k (Δx)²

• Any object being deformed.

What is the formula for KE?

½ mv²

(½ mv² - ½ mu²)

• Any object in motion.

What does the area under a Force Displacement graph represent?

The work done.

State the law of conservation of energy

In any closed system energy cannot be created or destroyed it can only be transferred from one store to another.

•  ΔE_t = 0

• It is a law of physics and empirical.

Empirical 

Based on observations or experiments.

Theoretical

Based on theories or hypotheses.

Power

The rate of work done.

Define efficiency

The ratio of how much useful energy was put in, to how much useful energy was put out.

What are the 2 formulas for efficiency?

η = useful work out / total work in

η = useful power out / total power in

What is a Sankey diagram and what do they show?

A Sankey diagram is a visual representation of energy transferred in applications/scenarios.

What can a resultant force on an object change?

The objects shape (compresses, extend, deform) and the objects velocity (speed and or direction).

Tension

The force exerted by a string, rope, cable, spring etc.

It is the same along all points

What law must all elastic objects obey?

They must all obey Hooke’s Law, where force is proportional to extension.

What is weight force?

Mass x gravitational field strength.