Presentation on theme: "1. How would the effort exerted by a backpacker over level ground compare to the effort in climbing a steep hill? 2. How would the weight of the backpack."— Presentation transcript:
1 1. How would the effort exerted by a backpacker over level ground compare to the effort in climbing a steep hill?2. How would the weight of the backpack affect the amount of force needed to move it?
2 1. The transfer of energy when a force makes an object move. Work and MachinesA. Work1. The transfer of energy when a force makes an object move.2. W = f ·d(Unit is a jouleor N ·m)Box being given energy3. Energy is transferredbetween objects whenwork is done.
3 B. Power1. The rate at which work is done.2. P = W / t3. Unit is the watt (1 joule / second)4. Btu = 1,055 watts(for heating and cooling units)5. Horsepower = 746 watts(for motors and engines)
4 1. A machine makes doing work easier. C. Using Machines1. A machine makes doing work easier.2. They may multiply the applied force.The car may weigh a lot, but you don’t have to use nearly that much force to lift it with a jack.
5 3. They may increase the distance over which a force is applied. In this case, the amount of force necessary to push the chair up the ramp was decreased.
6 The nail comes up as the person pulls to the side. 4. They may change the direction a force has to be applied.The nail comes up as the person pulls to the side.
7 D. Important terms for machines 1. Resistance – the force being moved (FR)2. Effort – the force being used to move a resistance (FE)3. Effort Distance – the distance the effort force moves through (de)4. Resistance Distance – how far the resistance moves (dr)
8 E. Work Calculations1. Work Input – the amount of work done on a simple machine.2. Win = FE • de3. Work output – the amount of work the machine actually does.4. Wout = FR • dr
9 F. Conservation of Energy 1. No machine can create energy, so Wout can never be greater than Win2. In reality, Wout is always less than Win because of friction producing heat; the heat had to come from the energy put into the machine.3. An ideal machine is theoretical; it does not take friction into account.4. Ideal machine: Win = Wout
10 G. Mechanical Advantage 1. MA is the number of times a machine multiplies the effort force.2. MA = FR / FE & MA = de / drH. Efficiency1. Measures how much of the work input is changed into useful output2. Efficiency = (Wout / Win) x 100%
11 3. Lubricants (such as oil and graphite) reduce friction & increase efficiency. Oil fills the space between surfaces so high spots don’t rub against each other.
12 d. IMA = effort arm / resistance arm I. The Simple Machines1. Leversa. 1st class:b. 2nd class:c. 3rd class:d. IMA = effort arm / resistance armFEFRFEFRFRFE
13 2. Pulleysa. Fixed pulley1) changes only the direction of a force2) always has IMA = 1b. Movable pulley1) attached to object2) IMA = 2
14 This strand does not count toward the IMA c. Block and TackleThis strand does not count toward the IMA1) system of fixed and movable pulleys2) IMA = number of strands supporting the resistance
15 3. Wheel and Axlea. IMA = rw / rab. Gears are modified forms of the wheel and axle
16 4. Inclined Planes: IMA = Ls / Lh 5. The Screwa. Modified inclined plane wrapped around a cylinderb. The pitch of the threading determines the IMA6. The Wedge: two inclined planes back-to-back