Grade 4 | Science | Unit 2 - Concept 3 - Lesson 2 - Basics of speed

Welcome dear students!
Speed:
It is the distance that an object travels in a certain amount of time.
Calculating the speed:
• To calculate the speed of any moving object, we can divide the distance that the object moves by the time taken to travel that distance as follows:
Speed = distance / time
So, we can define speed also as, distance per unit time.
The measuring unit of speed may be:
• Kilometer Per Hour (km/hr)
• Meter Per Second (m/sec)
Note
The speed of an object is not affected by the direction of this moving object.
Example:
If a car moves forward 5 meters in one second, then it moves backward 5 meters in one second, so its speed is still 5 meters per second.
Problems:
1. Amir runs 100 meters in 20 seconds. Calculate the speed of Amir.
Speed = distance / time
Speed= 100/ 20=5 m/sec
To compare the speed of two moving objects, we can use one of the following two ways:
1. Measure the distance that both objects travel in the same amount of time.
• The object that travels a greater distance in the same amount of time is moving at a greater speed.
• Example: If two runners run for 1 hour, where:
• The first runner travels 6 kilometers.
• The second runner travels 9 kilometers.
• So, the second runner is moving at a greater speed, because he travels a greater distance (9 km) in the same amount of time (1 hour).
2. Measure the time that both objects take to travel the same distance.
• The object that travels the same distance in a smaller amount of time is moving at a greater speed.
• Example: If two cars are racing 120 kilometers, where:
• The first car reach the end line of race in 1 hour.
• The second car reach the end line of race in 2 hours.
• So, the first car is moving at a greater speed, because it travels the same distance (120 kilometers) in a shorter time (1 hour).
• Now, let's study the relation between speed and kinetic energy.
Tools
• Toy truck
• Metric ruler
• Cardboard paper towel tube
• Paper cup
• Stopwatch
• Scissors
• Books
Steps
Part (1) : The relation between the speed and the angle of inclination.
1. Put one end of the tube on the top of two books, and the other end of the tube resting on the ground.
2. Record in a table the number of books used to set up the tube in the column "Number of books".
3. Roll the truck down the tube. Use the stopwatch to determine the time and record in the table how long the truck takes to travel to the end of the tube in the column "Time to travel".
4. Add one book to change the incline angle and repeat the steps, then add another book and repeat the steps again.
Part (2) : The relation between the kinetic energy and the angle of inclination.
1. Now, repeat the activity as in part (1), but place the paper cup at the bottom of the tube as shown in the opposite figure.
2. Measure the distance the cup moves each time after the truck rolls into it, and record in a table the distance that the cup travels in the column "Distance the cup traveled".
Observations
• As the angle of inclination increases, the speed of the truck increases as it takes less time to reach the end of the tube.
• As the angle of inclination increases the distance that the paper cup traveled increases.
Conclusions
• As the angle of inclination of a moving object increases, its speed increases.
• As the speed of a moving object increases, its kinetic energy increases.
• So, both speed and kinetic energy increase, as the angle of inclination increases.
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Mr. Raouf Ashraf