Dynamics - AQA A-Level Physics

Displacement

Distance in a given direction (vector)

Speed

Change of distance per unit time (scalar)

Velocity

Speed in a given direction (vector)

How can you find speed of a moving object at a certain point using an s-t graph?

By drawing a tangent and finding the gradient.

What does the gradient of a v-t graph tell you?

The acceleration

What does the area under the line on a v-t graph represent?

The total displacement

What is the difference between a distance-time graph and a displacement-time graph?

The gradient of a distance-time graph is the speed, whereas the gradient of a displacement time graph is the velocity.

What is the difference between a velocity-time graph and a speed-time graph?

The area under the line of a velocity graph represents displacement, whereas the area under a speed-time graph represents the distance

Newton’s First Law

An object will remain at rest or in constant motion unless acted on by a resultant force.

Newton’s Second Law

The rate of change of momentum is proportional to the resultant force acting on it. (F=ma)

Newton’s Third Law

When an object A exerts a force on an object B, object B exerts an equal and opposite for on object A.

3 Factors that affect the size of drag on an object

• Object’s shape (cross sectional area)

• It’s speed

• The viscosity of the fluid

Describe the 3 stages of an parachuter falling before opening their parachute

• The objects begins to accelerate through the air with no air resistance

• The air resistance increases and the acceleration decreases

• The parachuter reaches terminal velocity - air resistance and weight are equal

Conservation of energy

Energy cannot be created or destroyed, only converted from one form to another.

Work done

The energy transferred to an object when a force is applied on it.

How can we find the work done on a force-distance graph?

By finding the area underneath the line

4 ways in which energy can be transferred between objects

• Radiation

• Electrical work

• Mechanical work

• Thermal heating

Power

The rate of transfer of energy or the rate at which work is done.

Formula for efficiency of a machine

Useful energy transferred by the machine / energy supplied to the machine

Useful energy

Energy transferred for a purpose