Ch 6 Test: Controlling Heat Transfer

Please remove hats and hoods

Ch 7 Simple Machines

Science 14 and 10-4 with Mrs M

Please remove your hats

7.1 Many types of Energy

• We have already talked about thermal energy or heat

• Kinetic energy = energy of motion (recall temperature is the average of kinetic energy)

• What about the energy used in machines?

Many types of energy

• Energy is the ability to do work

Work = Force x distance

• W = F x d• Work is a form of energy measured in Newton

meter (Nm) or Joules (J)• Work is defined as a force applied over a

distance

Which requires more effort or force, a short/steep or a long/gradual ramp?

W = F x d

• A force of 20 N is required to lift a box. The box is lifted from the floor to a shelf that is 2m high. What is the amount of work done?

• W = F x d• W = 20 x 2• W = 40 Nm

W = F x d

• Pushing a wheelbarrow takes 8000 Nm of work. How much force was needed to move it 25 m?

Simple Machines

• Simple machines have one movement• The movement of an inclined plane/ramp is a

slide.• A ramp is an old simple machine

Work requires a FORCE input over a DISTANCE

No Work

Work being done by pedaling force uphill

Pushing against a wall is NOT work… because it’s not moving!

Quick Quiz #5

• Open book• Individual

Levers

• Lever: a rigid bar resting on a pivot, used to help move a heavy load/weight– Fulcrum= pivot point– Load= weight to be moved– Effort= force applied

LeversFulcrum in middle 1st class

Load/Weight in the middle 2nd classEffort/Force in the middle 3rd class

1st classEffort, Fulcrum, Load

1st class levers

1st classFulcrum in the middle

2nd Class LeverLoad or Weight in the middle

2nd class levers

2nd classLoad or weight in the middle

3rd Class LeversEffort or Force in the middle

3rd class levers

3rd class leverEffort in the middle

FLE 123

Why should a heavier person sit closer to the fulcrum on a teeter totter?

Center of massGirl’s Work = Boy’s Work

Girl’s Force x girl’s distance = Boy’s Force x boy’s distanceWeight(girl)x d = Weight(boy)x d

The little girl’s weight is 133 N and sits 0.5m from the middle of the teeter totter. How far

away does the boy sit if he weighs 265 N?

Weight(girl)x d = Weight(boy)x d133 x 0.5 = 265 x d

(133x0.5)/265 = d