physics Lesson Note On Speed, Velocity & Acceleration

Topic: Speed, Velocity & Acceleration

Subject: Physics
Class: SS1
Duration: 40 minutes

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Instructional Objectives

By the end of the lesson, students should be able to:

1. Define speed and velocity.
2. State the differences between speed and velocity.
3. Define acceleration.
4. Solve problems involving speed, velocity, and acceleration.
5. Explain uniform and non-uniform motion.

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Instructional Materials

• Stopwatch
• Measuring tape/meter rule
• Ball or toy car (to demonstrate motion)
• Graph/chart of velocity-time motion

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Lesson Content in Steps

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Step 1: Speed

• Speed is the distance covered per unit time.
• It is a scalar quantity because it has magnitude only (no direction).
• Formula:

  \text{Speed} = \frac{\text{Distance}}{\text{Time}}

• Example: If a car covers 100 m in 20 s,

  \text{Speed} = \frac{100}{20} = 5 \, \text{m/s}

• Uniform speed: covering equal distances in equal time intervals.
• Non-uniform speed: covering unequal distances in equal intervals of time.

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Step 2: Velocity

• Velocity is the rate of displacement with time.
• It is a vector quantity (has magnitude and direction).
• Formula:

  \text{Velocity} = \frac{\text{Displacement}}{\text{Time}}

• Example: A man walks 120 m north in 60 s.

  \text{Velocity} = \frac{120}{60} = 2 \, \text{m/s north}

Speed	Velocity
Scalar quantity	Vector quantity
Based on distance	Based on displacement
No direction	Has direction
Cannot be zero unless body is at rest	Can be zero even when body moves and returns to starting point

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Step 3: Acceleration

• Acceleration is the rate of change of velocity with time.
• It is a vector quantity.
• Formula:

  a = \frac{v - u}{t}

= acceleration,
= initial velocity,
= final velocity,
= time taken.

• SI unit: m/s².

• Positive acceleration: velocity increases with time.

• Negative acceleration (retardation/deceleration): velocity decreases with time.

Example: A car increases velocity from 10 m/s to 30 m/s in 5 s.

a = \frac{30 - 10}{5} = \frac{20}{5} = 4 \, \text{m/s}^2

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Step 4: Uniform vs Non-uniform Motion

• Uniform Motion: When a body moves with constant velocity (or covers equal distances in equal times). Example: a train moving steadily at 60 km/h.
• Non-uniform Motion: When a body moves with varying velocity (unequal distances in equal times). Example: a car in traffic or a ball rolling to rest.

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Step 5: Problem Solving Practice

Example 1 (Speed):
A man runs 400 m in 80 s. What is his average speed?

\text{Speed} = \frac{400}{80} = 5 \, \text{m/s}

Example 2 (Velocity):
A student walks 50 m east in 25 s. Calculate his velocity.

\text{Velocity} = \frac{50}{25} = 2 \, \text{m/s east}

Example 3 (Acceleration):
A car initially moving at 20 m/s stops in 10 s. Find its acceleration.

a = \frac{0 - 20}{10} = \frac{-20}{10} = -2 \, \text{m/s}^2

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Step 6: Summary

• Speed is the rate of distance covered with time (scalar).
• Velocity is the rate of displacement with time (vector).
• Acceleration is the rate of change of velocity with time.
• Motion can be uniform (constant velocity) or non-uniform (changing velocity).
• All these concepts are related through simple equations of motion.

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Evaluation Questions

1. Define speed and velocity.
2. State two differences between speed and velocity.
3. What is acceleration? Give its SI unit.
4. A car accelerates from rest to 25 m/s in 10 seconds. Calculate its acceleration.
5. Distinguish between uniform and non-uniform motion.

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Classwork

A car moves a distance of 200 m in 20 seconds and then increases its velocity from 10 m/s to 20 m/s in 5 seconds. Calculate:
(a) its average speed for the first motion,
(b) its acceleration for the second motion.

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Homework

1. A train moves with a velocity of 30 m/s. It slows down uniformly to 10 m/s in 10 s. Find its retardation.
2. A student walks 300 m due north in 5 minutes. Calculate his velocity in m/s.
3. Differentiate between speed, velocity, and acceleration using examples.

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