EQ: How do simple machines make work easier? Work and Power EQ: How do simple machines make work easier? Get free 5 day trial of link, move to the end of PPT

Work, a definition The word work has a different meaning in science than it does in everyday life. In science, work is when you exert a force that makes an object move in the same direction as the force. Work is using a force to move an object a distance Force = a push or a pull

Work, a definition Work always makes an object move a distance, and the object must move in the same direction as the force. If the object does not move, you have not done work, no matter the force exerted.

Work, a definition The motion for work must be in the same direction as the force.

Work Examples Pushing a child on a swing You are moving the child over a distance in the direction of the force Pulling books out of your book bag. You are moving the book over a distance in the direction of the force.

Work Non-examples Pushing on a wall Pushing a car stuck in the snow. Holding weights on your shoulders Holding a kitten over your head When a pencil is sitting on a table, not moving Carrying your books to class

Work, Non-examples The reason why you didn’t do work when you carried your books to class is because the force exerted must be in the same direction as the object’s motion.

Work, Non-examples When you carry books to class, the force is exerted upward. But the motion of the books is toward the classroom. Since the force is exerted is upward, and the motion is toward the classroom, scientifically, no work is done.

The Earth revolving around the Sun… Work or no work? No work! The Sun’s gravitational force pulls the Earth toward the sun Inertia wants the Earth to move in a straight line. The two forces work together to keep the Earth in the Sun’s orbit. But since the Earth is NOT moving in the direction of either force, no work is being done! Earth orbiting the Sun (non-example)

Work/No Work Lifting a box of newspapers Work – object moved a distance in the direction of the force You hold a heavy piece of metal in one place No work – object did not move a distance You roll a suitcase through the airport Work – object moved an object a distance in the direction of the force Carrying a suitcase through an airport No work --- an object was moved, but the force is upward while you are moving forward

AP: Balloon Fight A group of students gather for some funduring their summer break form school. Kendall and Jacob have a balloon fight during one of those “lazy” days of summer. Marie, Gary and Louise remember a video about work that their science teacher showed them before they left for vacation. Marie says, “If Kendall throws a water balloon at Jacob, there is no work being done. It’s just boys being boys” Gary says, “If Kendall throws a water balloon at Jacob, there is work being done by Jacob because he has to run” Louise says, “If Kendall throws a water balloon at Jacob, there is work being done because Kendall had to exert a force that made the water balloon travel a certain distance to hit Jacob” Which one of them is correct, and why?

Calculating Work The amount of work depends on two things: The amount of force exerted The distance the object moves due to the force.

Calculating Work It takes more work to move a heavier object than it does to move a light object. It takes more work to move an object a long distance than it does to move an object a short distance.

Calculating Work Work = Force X Distance Work can be calculated by using this formula Work = Force X Distance The unit of measurement for force is a newton (N) 1 N is required to lift a small lemon The unit for distance is meters (M), kilometers (km), miles , etc. The unit to measure work is the joule

Calculating Work Practice Peggy uses a force of 40 N to move her grocery basket 18 meters. How much WORK did she perform? 720 joules Billy runs out of gas and has to push his 8000 N stalled car a distance of 25 meters to the nearest parking lot. How much WORK does Billy perform during this time? 200,000 joules

Power, a definition The amount of work done on an object is not affected by how long it takes to do the work. For example, when lifting a book out of your book bag to place on a table, the work you do is the weight of the book times the distance to the table. How quickly you move the book does not figure into the equation.

Power, a definition But time is important when you talk about power. Power is the work done on an object in a certain amount of time. It means doing the same amount of work in less time

Power, a definition You would need more power to quickly lift your book out of your book bag because it would take you less time to do the work.

Power, examples Greater engine power of a car = faster acceleration Running vs. walking up stairs Using a leaf blower vs. raking Biking vs. walking

Power = Force X Distance / Time Calculating Power Power can be calculated using this formula: Power = Work/Time Since Work = Force X Distance, the formula of: Power = Force X Distance / Time Is more commonly used Power is measured in watts

Calculating Power Example Power = Work/Time Power = Force X Distance / Time Steps to solving: 1. Figure out the work in joules 8000 N X 25 m = 200,000 joules 2. Divide the amount of work by time 200,000 joules/5 minutes 3. Answer Power = 40,000 watts or 40 kilowatts I kilowatt = 1,000 watts Billy runs out of gas and has to push his 8000 N stalled car a distance of 25 meters to the nearest parking lot. It takes him 5 minutes to push the car. How much POWER did Billy exert?

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