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Physics Revision Notes

Unit 2.1 Speed, Distance and Acceleration

Calculating Speed

Speed is defined as the distance moved per unit time, described by the formula:
s = \frac{d}{t}

Where:

  • s = speed

  • d = distance

  • t = time

Units:

  • Distance = metres (m)

  • Time = seconds (s)

  • Speed = metres per second (m/s)

Other Forms of Speed Equation:

  1. d = s \times t

  2. t = \frac{d}{s}

Examples:

  1. Example 1: A school bus moves 1600 metres at an average speed of 12.5 m/s, how long did the journey take?

    • t = \frac{d}{s} = \frac{1600}{12.5} = 128 ext{ s}

  2. Example 2: An electron moves at a speed of 2500 km/s for 1 minute. How far does it travel?

    • Convert speed to m/s: 2500 ext{ km/s} = 2500 \times 1000 = 2500000 ext{ m/s}

    • Calculate distance:

      • d = s \times t = 2500000 \times 60 = 150000000 ext{ m}

Calculating Acceleration

Acceleration is the change in velocity (or speed) per second, described by:
a = \frac{\Delta v}{t}
Where:

  • a = acceleration

  • \Delta v = change in velocity

  • t = time

Units:

  • Change in Velocity = metres per second (m/s)

  • Time = seconds (s)

  • Acceleration = metres per second squared (m/s²)

Examples:

  1. Example 1: A cyclist increases speed from 5 m/s to 19 m/s in 7 seconds. Find acceleration.

    • a = \frac{\Delta v}{t} = \frac{(19 - 5)}{7} = \frac{14}{7} = 2 ext{ m/s²}

  2. Example 2: An oil tanker decelerates at 0.04 m/s² from 12 m/s.

    • t = \frac{\Delta v}{a} = \frac{12}{0.04} = 300 ext{ s} (5 minutes)

  3. Example 3: A football moves forwards at 12.4 m/s and accelerates at 48.0 m/s² for 0.45 s. What is the final speed?

    • Change in speed: \Delta v = a \times t = 48.0 \times 0.45 = 21.6 ext{ m/s}

    • Final speed: 12.4 + 21.6 = 34.0 ext{ m/s}

Motion Graphs

Distance-Time Graphs

  • Rule: The slope of a distance-time graph indicates speed.

    • Steep Line: High speed

    • Less Steep Line: Lower speed

    • Flat Line: Stationary

  • Examples: Segment AB shows constant speed; segment BC shows stationary at 60m.

Velocity-Time Graphs

  • Rules:

  1. The slope equals acceleration.

  2. The area under the graph equals distance travelled.

  • Example Calculations:

    • Segment with constant acceleration: calculate average speed.

- Use area of shapes to determine distance.

Unit 2.2 Newton's Laws

Forces: A force is a push or pull. Measured in newtons (N).

Resultant Force

The resultant force is the overall force acting on an object when all individual forces are combined and considered.

Newton's Laws

  1. First Law: A body will remain at rest or in uniform motion unless acted upon by a resultant force (inertia).

  2. Second Law: F = \frac{\Delta p}{t} or simplified F = m \times a.

3. Third Law: For every action, there is an equal and opposite reaction.

Unit 2.3 Work and Energy

Work Done

W = F \times d
Where:

  • W = work done (Joules, J)

  • F = force (Newtons, N)

  • d = distance (metres, m)

Energy Types

  1. Kinetic Energy (KE): KE = \frac{1}{2} mv²

  2. Potential Energy (PE): PE = mgh
    Where:

  • m = mass (kg)

  • g = gravitational field strength (N/kg)

  • h = height (m)

Conservation of Energy

Energy cannot be created or destroyed but transferred from one form to another.

Unit 2.4 Further Motion Concepts

Equations of Motion

  • Basic equation for speed: s = \frac{d}{t}

  • Advanced equations when acceleration is constant:

    1. v = u + at

    2. s = ut + \frac{1}{2} a t²

    3. v² = u² + 2as

Displacement and Direction

Displacement has direction; ensure vectors are considered in calculations.

Unit 2.5 Stars and Planets

Life Cycle of Stars

  • Low Mass Stars: Main sequence -> Red giant -> Planetary nebula -> White dwarf.

  • High Mass Stars: Main sequence -> Red supergiant -> Supernova -> Neutron star or Black hole.

Nuclear fusion: Key source of a star's energy. Also produces heavier elements in supernova explosions.