Speed, Displacement, Velocity and Acceleration

1. Speed

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Speed: How fast something is moving. It is the distance travelled per unit of time. Measured in metres per second (m/s) or kilometres per hour (km/h).

Formula: Speed = Distance / Time
Example: If a car travels 100 km in 2 hours, its speed is 50 km/h.

2. Distance

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Distance: The total length of the path travelled by an object. It is a scalar quantity (only magnitude, no direction). Measured in metres (m) or kilometres (km).

The total path covered by a moving object.
It does not depend on direction.
Example: If you walk around a track that is 400 metres, your distance is 400 metres.

3. Velocity

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Velocity: The speed of something in a given direction. It is a vector quantity (has both magnitude and direction). Measured in metres per second (m/s).

Formula: Velocity = Displacement / Time
Example: If a car moves 100 metres east in 10 seconds, its velocity is 10 m/s east.

4. Displacement

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Displacement: The straight-line distance from the starting point to the end point, including direction. It is a vector quantity. Measured in metres (m).

The shortest path from the start to the end point, in a straight line.
It includes direction.
Example: If you walk 3 metres north and then 4 metres east, your displacement is 5 metres northeast.

5. Acceleration

Formula: Acceleration = (Final Velocity - Initial Velocity) / Time
Example: If a car speeds up from 0 to 20 m/s in 10 seconds, its acceleration is 2 m/s².
Acceleration can be positive (speeding up) or negative (slowing down, also called deceleration).

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Acceleration: The rate at which velocity changes over time. It is a vector quantity. Measured in metres per second squared (m/s²).

6. Important Points to Remember

Speed vs. Velocity:

Speed is how fast you are going.
Velocity is how fast and in which direction you are going. Distance vs. Displacement:
Distance is the total length of your journey.
Displacement is the straight-line distance from start to end point.

7. Practical Examples

1. Calculating Speed:

If a cyclist covers 30 km in 1 hour, their speed is 30 km/h. 2. Measuring Distance:
If you walk 2 km to school and 2 km back, your distance is 4 km.

3. Finding Velocity:

If a boat travels 500 metres south in 100 seconds, its velocity is 5 m/s south. 4. Determining Displacement:
If you travel 3 km north and then 4 km east, use the Pythagorean theorem to find displacement. Displacement = 5 km northeast.

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Exam Tip! Make sure to practise past exam questions with these calculations for a good understanding of the concept.

Speed and distance are scalar quantities, focusing only on magnitude. Velocity and displacement are vector quantities, considering both magnitude and direction.

8. Mandatory Experiment

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To measure the acceleration of an object

Hypothesis: Acceleration of a moving object can be gotten mathematically. The steeper the slope the faster the acceleration.

Method:

Make a slope as shown in the diagram.
Record the length of the track.
Place a toy car on the track and record using a stopwatch the time it takes from top to bottom.
Insert values into the acceleration formula and calculate the acceleration.
Ensure the units are correct.
Repeat experiment using different heights for the track. Compare and contrast the results.

Result:

The steeper the slope the faster the acceleration. Conclusion:
The steeper the slope the faster the acceleration due to gravity. Notes:
Repeat with different cars/objects.
Repeat using different surfaces (smooth or rough). Formula:

Acceleration = \frac{V_2 - V_1}{T_2 - T_1}

Units: cm/s²

Speed, Displacement, Velocity and Acceleration Simplified Revision Notes for Junior Cycle Science

Speed, Displacement, Velocity and Acceleration

1. Speed

2. Distance

3. Velocity

4. Displacement

5. Acceleration

6. Important Points to Remember

7. Practical Examples

8. Mandatory Experiment

To measure the acceleration of an object

500K+ Students Use These Powerful Tools to Master Speed, Displacement, Velocity and Acceleration For their Junior Cycle Exams.

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