2. MachinesMachines 1 Properties of a machine Transfer energy from one place to another place Change the direction of a force Change the magnitude of a force Can never change the magnitude of energy Next Slide Examples Diagram

3. MachinesMachines 2 Terms related to a machine Effort (the force we apply to the machine) Load (the force that the machine supplies to move the desired object Input energy = work done by the effort = effort  distance moved by the effort Output energy = work done on the load = load  distance moved on the load Next Slide

4. MachinesMachines 3 Terms related to a machine Since output energy is always smaller than input energy, the efficiency is always smaller than 100 %. Loss energy may become sound and internal energy due to friction or be used to increase the P.E. the movable part of the machine. Next Slide Calculation

5. MachinesDifferent Machines 1 Various kinds of machine A machine which enables a heavy load to be raised by a small effort, is a force multiplier.. Various kinds of lever : nut cracker, scissors, single- wheel cart Next Slide Diagram Inclined plane Wheel-and-axle Calculation

6. MachinesDifferent Machines 2 Various kinds of machine Screw-jack Hydraulic press Next Slide Calculation Single pulley Calculation Gears Bicycle Calculation

7. END of Machine

8. Machines Next Slide Machines 1 Transfer energy from one place to another energy Change the direction of a force tension upwards pulling force downwards

9. Machines Click Back to Machines 1 Change the magnitude of a force Back to heavy load small effort

10. Machines Next Slide Machines 3 By making use of a lever, an effort 20 N is used to raise a block (mass 5 kg) by 5 cm as shown in the following diagram. What is the efficiency of this lever? How much energy has been lost? 20 N mass : 5 kg 5 m 1 m pivot

11. Machines Next Slide Machines 3 effort 1 m pivot 5 m 0.25 m 0.05 m

12. Machines Click Back to Machines 3 Back to

13. Machines Next Slide Different Machines 1 Nut Cracker Scissors effort load pivot nut effort load pivot paper

14. Machines Click Back to Different Machines 1 Single-wheel cart Back to load effort pivot sand

15. Machines Next Slide Different Machines 1 A block (mass 20 kg) is pulled by a force 100 N upwards along the incline plane shown. Find the efficiency of the machine and the friction acting on the block by the plane. 5 m 2 m rough incline plane 100 N

16. Machines Click Back to Different Machines 1 Back to

17. Machines Next Slide Different Machines 1 2 kg of water is raised in a bucket with mass 0.5 kg by a wheel-and-axle machine as shown in the following figure. Assume that the handle has been turned by an effort 10 N for one round, find its efficiency. 0.3 m 0.1 m 10 N water 2 kg bucket 0.5 kg

18. Machines Click Back to Different Machines 1 Back to In this case, only the water is considered as the load. The bucket is thought as one part of the machine. Therefore, when we consider the energy gained by the load, we only consider the P.E. gained of the water.

19. Machines Next Slide Different Machines 2 A screw jack is used to raise the load (mass : 1000 kg) by an effort 50 N as shown in the following figure. The height of the pitch is 1 mm and the length of the handle is 0.5 m. Find its efficiency. Such an machine needs a LOW efficiency, why? Load :1000 kg 0.5 m height of pitch : 1 mm Effort : 50 N

20. Machines Click Back to Different Machines 2 Back to Assume that the handle has been turned for one round. The load would be raised by a height equal to the height of pitch. Small efficiency means the energy lost due to friction is large. Therefore, the friction of this machine is very large. If we remove the effort, the friction is large enough to prevent the load from falling downwards.

21. Machines Next Slide Different Machines 2 A hydraulic press is used to move a load (mass : 100 kg) upwards for 1 cm as shown. The distance pushed by the effort 20 N is equal to 1 m (Why?). Find its efficiency. oil 1 m 1 cm effort 20 N load 100 kg

22. Machines Click Back to Different Machines 2 Back to It is very difficult to compress oil. Therefore, the volume of oil transferred to the column with the load remains the same.

23. Machines Next Slide Different Machines 2 A fixed pulley is used to move an load 20 kg upwards by an effort 250 N. The load has been raised by a height 1 m. Find its efficiency. load : 20 kg effort : 250 N

24. Machines Click Back to Different Machines 2 Back to The tension in the string holding the load is not equal to 250 N. It was because there is friction between and the string and the pulley.

25. Machines Next Slide Different Machines 2 A bicycle has the following dimensions: Find the distance moved by pedal and the wheel respectively if the crank has been turned for one round. Do you think that this machine is a force multiplier? 0.50 m 0.25 m 18 teeth 36 teeth

26. Machines Click Back to Different Machines 2 Back to In this case, the distance moved by the effort (pedal) is much shorter than the load (bicycle). Therefore, it is not a force multiplier. Bicycle is a machine that cannot save force. However, it can greatly increase the distance moved.