__PHYSICS WORK2:__

Make sure you have finished:

Reading
Sec 5-1, 5-2

Notes
on types and sources of energy

Science
Sleuths Collapsing bleachers with force diagram(handed in)

Energy
transformations for each time period (handed in)

Sec
Review 5-1 pg 171 (checked off)

__Work by
Constant Force__

Work = Force
* Dist * cos θ

•Example: You pull a 30 N chest 5
meters across the floor at a
constant speed by applying a force of 50 N at an angle of 30 degrees. How much
work have you (Tension) done?

Where did the
energy go?

*Work =
Force * Dist * cos θ = 50 N * 5 m * cos (30) = 43.3N *5m = 216 N m= 216
Joules*

•Example: You pull a 30 N chest 5
meters across the floor at a
constant speed by applying a force of 50 N at an angle of 30 degrees. How much
work did gravity do?

*Gravity did 0 work!*

•How much work did
friction do?

*Friction pulled with 43.3 N of force (opposite the
pull) so it was -216 Joules of Work*

Pull a block
horizontally for the same distance at a constant speed, with a scale at three
different angles and calculate the work in each case.

Work Lifting a Cart

•Going
straight up: Going
up ramp:

work = force
· distance work = force
· distance

•The work is the
same, either way!

Ramp
partially supports object’s weight Ramp
exchanges force for distance

Overall work done is unchanged

Investigation:

What
occurs when a machine does work on an object?

Calculate the
work in and the work out of a lever with two different masses balanced.

Try to
explain the difference.

Physics Concept Mechanical
Advantage

–Doing the
same amount of work

–Redistributing
force and distance

HW: Practice
5A problems Start Reading 8-4