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
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