1. PSAA Curriculum Unit Physical Science Systems

2. Problem Area Energy and Power Systems

3. Mechanical Power Transmission Lesson

4. What are some various agricultural applications that utilize mechanical power? What is the location of the power source and is the power applied at the rear axle? Is the speed and direction of the applied power the same as that of the source?

5. Learning Objectives Define force, torque, work, power, and energy and explain their relationship to each other and mechanical power transmission. Determine the relationship between diameter and number of teeth on a gear or sprocket and the speed and torque of the gear or sprocket.

6. Learning Objectives (cont.) Apply the Law of Conservation of Energy to power, torque, and speed relationships for mechanical power transmission.

7. Terms Acceleration Energy Force Gear Gear ratio Horsepower Kinetic energy Mass Newton Newton’s second law Potential energy Power RPM Torque Torque wrench Watt Work

8. What is the definition of force, torque, work, power, and energy and how do they relate to each other? Force can be defined as a push or pull that tends to start, stop, or change the direction of motion of an object. Force will vary depending upon gravitational forces. That is the reason our weight can vary from the earth to the moon due to the lower amount of gravitational pull on the moon thus making us weigh less on the moon versus the earth.

9. Mass However, mass (the amount of matter in an object) is the same no matter what location we are at on this planet or any planet. Gravity is a force that acts upon an object. The more mass an object has, the greater the force of gravity that acts upon the object.

10. Acceleration Force causes acceleration. The more force you apply to an object, the greater the rate of acceleration.

11. Newton’s Second Law Newton’s Second Law summarizes that the acceleration of an object is directly proportional to the force applied to the object and inversely proportional to the object’s mass. The more mass and object contained, the lower the rate of acceleration.

12. Newton To honor Sir Isaac Newton, the newton was adopted as the SI unit of force. One newton of force can accelerate one kilogram of mass at a rate of one meter per second per second.

13. Torque The force that tends to cause objects to rotate or turn is torque. When we use a wrench, we apply force to the handle. This force creates rotary motion or torque on the nut, which turns the nut to tighten or loosen.

14. Torque When calculating torque, the force applied is multiplied by the distance from the center (radius). English units of torque are inch-pounds or foot-pounds. The SI units are expressed as newton- meters, in honor of Isaac Newton.

15. Torque A torque wrench is used by a mechanic to tighten nuts and bolts to prevent them from loosening during engine vibration. The torque wrench can be adjusted to deliver the recommended amount of force to cylinder head bolts on a lawnmower engine without over tightening.

16. Torque If the wrench is one foot long and we apply 100 pounds of force on it when tightening, we are generating 100 foot-pounds of torque.

17. Work Work is the application of force to an object that causes the object to move in the direction of the force being applied. Lifting an object from the ground and placing it on a shelf is an example of work. The force being applied equals the weight of the object being lifted and the distance equals the height from the ground to the shelf.

18. Work Work equals force multiplied by distance. The units most often used to express work are foot-pounds or newton-meters. Work is energy that has been used.

19. Work Power is a measure of how quickly work can be done. Power equals work divided by the time. The SI (International System) unit for power is the watt.

20. Work One watt is equal to one newton-meter of work completed per second (N×m/s). If we pushed on an object with one newton of force, and moved it at a speed of one meter per second, our power output would be one watt (1 N × m/s).

21. Work A horsepower is equal to 746 watts. One horsepower is equivalent to 550 footpounds or work performed in one second or 33,000 foot-pounds of work done in one minute.

22. Energy Energy is the capacity to do work. Energy is a measure of how long you can sustain your power output.

23. Energy Potential energy is waiting to be converted to power. Compressed springs, gasoline, food in your stomach, a skier at the top of the slope, are all examples of potential energy.

24. Energy Kinetic energy is energy of motion. Any object that is in motion has kinetic energy. The more an object weighs, and the faster the object is moving, the greater the kinetic energy the object possesses.

25. Belt Velocity and Belt Force

26. What is the relationship that exists between the diameter and number of teeth of a gear and the speed and torque of the gear? A gear is a toothed wheel used to transmit power. Gears are used for four main reasons: 1) reverse the direction of rotation, 2) increase or decrease the speed of rotation, 3) move rotational motion to a different axis, and 4) keep the rotation of two axes synchronized.

27. Gears The gear ratio is determined by the distances from the center of the gear to the point of contact. If one gear is three times the diameter of the other, the ratio would be 3:1. This means that for every one revolution of the larger gear, the smaller gear will rotate three times in order to cover the same distance as the larger gear.

28. Gears (cont.) The majority of gears contain teeth. The teeth have three advantages on gears: 1) maintain synchronization and prevent slippage, 2) eliminate the concern about slight imperfections in diameter and circumference, and 3) make it possible to calculate exact gear ratios by counting the number of teeth and divide.

29. Gears (cont.) For example, if one gear has 50 teeth and the other gear has 25 teeth, the gear ratio between the two gears is 2:1.

30. Gears (cont.) Gears have many uses in mechanized devices. One of their most important uses is to provide gear reduction to help with power and torque requirements. A small motor is usually spinning fast enough to provide speed and power but not enough torque.

31. Gears (cont.) Gear reduction can be implemented in a device to reduce the output speed and subsequently increase the torque of the machine. If the power is constant in a machine, torque and speed are inversely related, meaning that a reduction in one will result in an increase in the other.

32. Gears (cont.) The diameter and number of teeth on a gear or sprocket is also inversely related to speed, meaning the larger gear with more teeth will spin at a slower speed. Speed of gears is measured in revolutions per minute (RPM).

33. What is the Law of Conservation of Energy and how does it affect power, torque, and speed relationships? Energy cannot be created or destroyed. Whenever work is done, the work appears as potential energy, kinetic energy, and horsepower, or the combination of all three.

34. Law of Conservation of Energy The energy input to a system must equal the energy output. The horsepower of most power sources used for agricultural applications is finite. Trade-offs must be made between torque and speed (RPM) when the power is transmitted.

35. Review/Summary What is the definition of force, torque, work, power, and energy and how do they relate to each other? What is the relationship that exists between the diameter and number of teeth of a gear and the speed and torque of the gear? What is the Law of Conservation of Energy and how does it affect power, torque, and speed relationships?