Understanding Work and Energy

Work
1. Work is defined as the product of the applied force and the displacement of an object in the direction of the applied force.
2. W = F x d
3. W= work done, F = force applied, d = displacement in the direction of force.
4. SI unit for work = Joule (J), other unit = Nm
5. Work is not done when:

• The object is stationary or not moving
• No force is applied on the object in the direction of displacement.
• The direction of motion of the object is perpendicular to that of the applied force.

6. When work is done to an object, energy is transferred to the object.


Energy (Energy is the capacity to do work)
1. Energy exists in different forms: kinetic energy, gravitational potential energy, elastic potential energy, sound energy, heat energy, light energy, electrical energy and chemical energy.
2. The unit for energy is Joule (J) – same as work
3. The work done is equal to the amount of energy transferred.
4. Kinetic energy is the energy of an object due to its motion.
5. Kinetic energy or work done is given by:

• a. ½ mv²
• b. M = mass, v = velocity
• c. Unit: Joule

6. Gravitational potential energy is the energy of an object due to its higher position in the gravitational field.

• E = mgh
• M = mass, g = acceleration due to gravity, h = height in metre

The Importance of Speed and Velocity in sports.

The Best Explanation from Grade 7 students

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Written by : Brigitta, Kevin Dwi, Raissa [7a]

Speed and velocity is very important and need to be included in sports. They have many useful benefits that many people need in sport. For instance, as an example, we need to know our speed and velocity in running and control it so we will not get exhausted quickly. If people can control their speed, they will not have really large amount in energy.

Speed and velocity is also needed in sports such as baseball. We need to know speed and velocity in baseball to predict when the ball will arrive (speed of the ball) and the direction too. This skill is very needed for the batter so that he or she can predict the right time, the strength and the direction when hitting the ball. This is why speed and velocity is very important.

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Written by : Celine, Darwin, Franklin and Kevin [7b].

It is important because we need skills that are connected to speed and velocity in sports. When we are playing sports like football, we need to pass the ball, run, we need power and that is connected to speed and velocity. When we want to pass the ball, we need speed and velocity so no one will keep up with you and results that no one will block your passing. When we are running, we can know the speed and velocity we are running and without speed, you will totally lose. When we need power, the faster you are, the stronger you are and the stronger you are, the more possibilities of winning. We can control the speed and velocity and that helps us in sports. In conclusion, speed and velocity is really important.

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Written by Clarissa, William, Reyna and Belinda [7c]

In the running competition, you have to know the speed. Cyclist needs speed so that they know their speed. In a running race, you need to know that speed so that you know the winner. We need to know the velocity when we are swimming so we can defeat others. In car racing, we need to know the speed that is shown by speedometer, so we don’t drive too fast and won’t cause bad damage. We need to know the velocity of badminton ball so we can hit the ball. So, in conclusion there are so many importance of speed and velocity in Physical Education.

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Written by Hans, Tirta, Angeline, Selma [7c]

For example in sport such as racing car. In the car they give the speedometer to read how fast the car is running. Velocity is used to know where the car is going to. Speed is importance so we know how fast is an athlete run per minute and velocity is used to know where the athlete is running. In soccer speed is used for player to run faster in the field so the player will get the ball and velocity is used to know the player direction so we can know to whom we pass the ball.

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