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