Unit 4 Mechanics

What is a scalar?

A quantity with only magnitude

What is a vector?

A quantity with magnitude and direction

What are examples of scalars?

Distance, speed, mass, temperature, energy

What are examples of vectors?

Displacement, velocity, force, acceleration

How is the resultant vector found?

Pythagoras

How is the direction of a vector found?

Trigonometry

When should a scale diagram be used?

When vectors are at angles other than 90

What is resolving vectors?

Using trigonometry to find the vertical and horizontal components of a vector

What is a moment?

The turning effect of a force

What is the formula for the moment of a force?

Moment = Force x Perpendicular distance to line of action of force from the point

What is a couple?

A pair of coplanar forces (meaning they are forces within the same plane) where the two forces are equal in magnitude but act in opposite directions

How is the moment of a couple found?

By multiplying one of the forces by the perpendicular distance between the lines of action of the forces

What is the principle of moments?

For an object in equilibrium the sum of anticlockwise moments about a pivot is equal to the sum of clockwise moments

What is displacement?

The overall distance and direction travelled from the starting position

What is velocity?

The rate of change of displacement

What is acceleration?

The rate of change of velocity

What is the centre of mass of an object?

The point at which an object's mass acts. If an object is described as uniform it's centre of mass will be exactly at its centre.

What is instantaneous velocity?

The velocity of an object at a specific point in time

How can instantaneous velocity be found?

By drawing a tangent to the graph at the specific time and calculating the gradient

What is average velocity?

The velocity of an object over a specified time frame

What is uniform acceleration?

Where the acceleration of an object is constant

What is projectile motion?

When the vertical and horizontal components are independent so they are evaluated separately using the uniform acceleration formula

What is free fall?

Where an object experiences an acceleration of g

What is friction?

A force which opposes the motion of an object and it is also known as drag or air resistance when considering friction experienced in a fluid

What do frictional forces convert kinetic energy into?

Heat and sound

What causes the magnitude of air resistance to increase?

The speed of the object increasing

What is lift?

An upward force which acts on objects travelling in a fluid

What causes lift?

When the object creating a change in direction of fluid flow and it acts perpendicular to the direction of fluid flow

Where does terminal speed occur?

When the frictional forces acting on an object and driving forces are equal therefore there is no resultant force and so no accelerating so the object travels at a constant speed

Which components of projectile motion is affected?

Both the vertical and horizontal

What is Newton’s first law?

An object will remain at rest or travelling at a constant velocity until it experiences a resultant force

What is Newton’s second law?

The acceleration of an object is proportional to the resultant force experienced by the object. F = ma

What is Newton’s third law?

For each force experienced by an object the object exerts an equal and opposite force

What is a free body diagram?

A diagram which shows all the forces that act on an object. The size of the arrow shows the size of the force in comparison to the other forces acting on the object

What is momentum?

The product of mass and velocity an object which explains interactions in nature

What is the formula for momentum?

mass x velocity

What is the law of conservation of momentum?

Momentum is always conserved in any interaction where no external forces act, which means the momentum before an event is equal to the momentum after. This is used to find the velocity of objects after collisions

What is an impulse?

The change in momentum which is equal to forceΔtime

What is the area of a force time graph equal to?

Change in momentum

What is an important application of calculating impulse?

Designing the safety features of cars e.g. crumple zones, which crumple on impact, seat belts, which stretch upon impact, and air bags all of which increases the impact time of the car or the passenger preventing injury

What are the two types of collisions and how are they different?

Elastic where both momentum and kinetic energy are conserved and inelastic where only momentum is conserved while some of the kinetic energy is converted into other forms and may be larger or smaller after a collision

What are examples of inelastic collisions?

When the objects stick together after the collision and an explosion as the kinetic energy after the collision is greater than before the collision

What is work done?

The force causing a motion multiplied by the distance travelled in the direction of the force

What is the equation for work done?

Work done = Force x distance x cosθ

What is the rate of work done equal to?

The rate of energy transfer

What is power?

The rate of energy transfer

How can work done be calculated when force is variable?

Finding the area under a force displacement graph

What is efficiency?

A measure of how efficiently a system transfers energy

What is the formula for efficiency?

Useful output power/input power

What is the principle of conservation of energy?

Energy cannot be created or destroyed but can be transferred from one form to another. Therefore the total energy is a closed system stays constant

What is the formula for change in gravitational potential energy?

ΔE_GP = mgΔh

What is the formula for kinetic energy?

E_k = 0.5mv²

When is the initial kinetic energy not equal to the maximum gravitational potential?

When the object has stopped in mid-air because the kinetic energy of the object is being transferred to the environment in the form of heat due to air resistance.