The student will learn about the main purposes and the basic components of all machines. SIMPLE MACHINES. SPH4C Findlay

Transcription

1 The student will learn about the main purposes and the basic components of all machines. SIMPLE MACHINES SPH4C Findlay

2 What do you think of when you hear the word machine?

3 Simple Machines Machines created thousands of years ago and even the machines used today are still based on basic machines. Tools such as arrows (wedges) and ramps (inclined plane) are examples of simple machines.

4 Simple Machines A Machine is a device that helps perform tasks. It is designed to achieve at least 1 of the 5 main functions.

5 The Purposes of Machines Change energy from one form into another. Example: hydroelectric converts the energy of falling water into electrical

6 The Purposes of Machines Transfer forces from one object to another. Car transmission transfers the force from the motor to the wheels

7 The Purposes of Machines To reduce the amount of force that is required for a job.

8 The Purposes of Machines To modify the speed of something.

9 The Purposes of Machines To change the direction of motion. Flag pole pull down on the rope to raise the flag by a pulley system.

10 The Purposes of Machines It is usually a trade-off between force and speed For Example A block and tackle makes it easier to lift a heavy object but it rises more slowly

11 The Purposes of Machines A ramp makes it easier to lift something but you have to move it farther to get it to the same height.

12 The Components of Machines Complex Machines are known as compound machines Compound machines are made of

13 Simple Machines: Lever Family A lever is a rigid bar that can rotate freely around a support called a fulcrum.

14 Simple Machines: Lever Family Levers are divided into three classes, depending on the position of the load, effort force, and the fulcrum.

15 Simple Machines: Lever Family

16 Simple Machines: Lever Family An effort force, F E, is a force applied to one part of a lever to move a load at another part; the load exerts a load force, F L. The perpendicular distance from the fulcrum to the effort force represents the effort arm, symbol d E, and the perpendicular distance from the fulcrum to the load force represents the load arm, symbol d L. d L

17 Simple Machines: Lever Family The Wheel and Axel Apply force to the wheel (makes it easier) Apply force to the axel (makes it go faster)

18 Simple Machines: Lever Family The Pulley This one changes the direction of the force

19 Simple Machines: Lever Family Gears These also change the direction of motion

20 Simple Machines: Inclined Plane Family Basic Inclined Plane - A ramp that increases the load that can be raised by an effort force.

21 Simple Machines: Inclined Plane Family Screw an inclined plane wrapped around a central shaft.. Seven Archimedes screws pump wastewater in a treatment plant in Memphis, Tennessee, USA. Each of these screws is 96 inches (2.44 meters) in diameter and can lift 19,900 gallons per minute

22 Simple Machines: Inclined Plane Family Wedge Two inclined planes back to back that increases the applied or effort force.

23 What is the Simple Machine? fulcrum Lever

24 What is the Simple Machine? Inclined Plane

25 What is the Simple Machine? Screw

26 What is the Simple Machine? Pulley

27 What is the Simple Machine? Lever - handles Wedgeblades

28 What is the Simple Machine? Lever (handles) Wedge (blades) Gears

29 The student will be able to solve problems involving torque, force, load-arm length, and effort-arm length as they relate to levers. TORQUE SPH4C Findlay

30 Feeling Torque When a force or set of forces causes a rigid body to rotate, we say a torque has been applied. Torque the turning effect caused by a force on a rigid object around a axis or fulcrum, symbol T; it is measured in Newton-meters, or Nm; it can be called a moment force.

31 Torque on Doors Every time you open a door, you are producing a torque on the door. A small force applied far from the hinges can produce the same amount of torque as a large force applied closer to the hinges. Distance Distance

32 Torque In order to create the largest amount of torque possible when pushing on the door, the force generated must be at a 90 degree angle to the door.

33 Magnitude of Torque The amount of torque produced depends on two factors. 1. The magnitude of the force (F) applied to the rigid object. 2. The distance (d) between the force and the axis or fulcrum.

34 Amount of Torque Using the symbol T for the magnitude of torque, the following statements hold true: T increases as F increases ( T F) T increases as d increases ( T d) Torque = force x distance or T = Fd (where F is perpendicular to the ridge object)

35 Example Problem Calculate the torque of a wrench experiencing a force of 84 N, a distance of 0.35 m away from the bolt. F = 84 N d = 0.35 m T =? T = Fd T = 84 N 0.35 m T = 29 Nm the magnitude of the torque on the wrench is 29 Nm.

36 Torque on Levers Two torques can be calculated for a lever: the effort torque (T E ) and the load torque (T L ). The associated distances are the effort distance, or effort arm (d E ), and the load distance, or load arm (d L ). d E d L T L T E

37 Torque on Levers Effort torque = effort force x effort arm T E = F E d E Or Load Torque = load force x load arm T L = F L d L In each case, the force is perpendicular to the lever, which allows us to deal with magnitudes only, thus avoiding vector signs.

38 Example Problem A camper is using a large plank as a first class lever to move a rock. The effort force has a magnitude of 4.5 x 10 2 N, and the distance from the fulcrum to the effort force is 2.2 m. What is the magnitude of the effort torque produced? (ignore the mass of the plank) F E = N d E = 2.2 m T E =? T E = F E d E T = N 2.2 m T = Nm the magnitude of the effort torque produced is Nm.

39 Static Equilibrium of Levers The word static means at rest. A rigid object that is in static equilibrium is at rest in two ways. 1. It is not moving in any direction 2. It is not rotating

40 Law of the Lever When a lever is in static equilibrium, the magnitude of the effort torque equals the magnitude of the load torque.

41 Law of the Lever This law can be written in the equation form Effort torque = load torque Effort force x effort arm = load force x load arm F E d E = F L d L For this equation, only the magnitudes of the quantities are considered. This eliminates the need for positive or negative signs.

42 Example Problem A camper wants to mount a trailer on blocks for the winter. One corner of the trailer is lifted by applying an effort force using a 3.00 m steel bar. The trailer is applying a load force of 1.8 x 10 3 N, a distance of 0.45 m away from the fulcrum. Determine the magnitude of the effort force required (ignore the mass of the bar)

43 Example Problem F L = N d L = 0.45 m d E = 3.00 m 0.45 m d E = 2.55 m F E =? F E d E = F L d L F E = F Ld L d E F E = N 0.45 m 2.55 m F E = N the force needed to lift the trailer is N.

44 Law of the Lever For any rigid object, the law of the lever can be stated in more general terms based on which way it is turned. The clockwise torque is balanced by the counter clockwise torque. T CW = T CCW Where T CW = magnitude of the clockwise torque on an object around the fulcrum. Where T CCW = magnitude of the counter clockwise torque on an object around the fulcrum.