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What is Work?- Examples… Lifting weights, pulling a wagon, pushing a box across the floor and pushing a grocery cart
-What cause it? A force applied over the distance an object moves
WORK
W= F dVariables:
W = Work
F = Force
d = Distance
Units:
W = NewtonsmW = Joules
F = N
d = m
W= F d
Work can be positive or negative if the force opposes the motion of the object the work being done is negative. If the force is applied in the same direction as
the motion of the object the work being done is positive!
W= F d
A person is pushing a block with a force of 50N over a distance of 2 meters. What is the work done? F= 50 N d= 2m W= 50 N * 2 m = 100 N*m forward
What about…DIRECTION?
Direction matters!!The force being applied and the direction of the motion CANNOT be perpendicular for work to be done!
Horizontal…
Horizontal…
Vertical…
What about this?Work is done when the girl lifts the books because she applies a force in the upward direction and the books move up. The force is not perpendicular to the objects motion.
When she walks forward she is not doing work because the force being applied to the books is up. The direction of the motion motion is forward, since these are perpendicular, there is no work being done by the girl on the books
So…What is Work?
Work-Work is the…
Product of distance and the force …
In the direction an object moves.
W = Fd and in what direction!
Work problems
• 1. A woman lifts her 100-newton child up one meter and carries her for a distance of 50 meters to the child’s bedroom. How much work does the woman do?
• 2. How much work does a mother do if she lifts each of her twin babies upward 1 meter? Each baby weighs 90 newtons.
• 3.a You pull your sled through the snow a distance of 500 meters with a horizontal force of 200 newtons. How much work did you do?
• 3b. Because the snow suddenly gets too slushy, you decide to carry your 100-newton sled the rest of the way home. How much work do you do when you pick up the sled, lifting it 0.5 meter upward?
• 3c. How much work do you do to carry the sled if your house is 800 meters away?
• 4. An ant sits on the back of a mouse. The mouse carries the ant across the floor for a distance of 10 meters. Was there work done by the mouse? Explain.
