Physical Science Applications in Agriculture Unit Physical Science Systems

Problem Area Agricultural Mechanics and Machine Systems

Moving and Lifting With Simple Machines Lesson

How is each of these hand tools similar? / different? Show a pair of bolt cutters, tin snips, and scissors. Attempt one or more of these activities: –try pulling a large nail from a piece of hardwood, first with a nail hammer, and then with a wrecking bar or nail puller;

Learning Objectives 1.Identify the types (classes) of levers. 2.Determine the effects of lever design on lifting power. 3.Explain the relationship between levers and wheels. 4.Test the effectiveness of various pulley designs. 5.Calculate the mechanical advantage of an inclined plane.

Terms Effort Fulcrum Inclined plane Lever Load Mechanical advantage Pulley Wheels

What are the classes of levers? A lever is a rigid bar that turns around a pivot point, called the fulcrum. The force (effort) applied raises a weight or overcomes a resistance (load). tinkering_fulcrum.htm

The types of levers are based on the location of fulcrum, effort, and load. Class I lever The fulcrum positioned between the load and the effort. Lever increases the effort and reverses the direction of motion.

Class II Lever The fulcrum positioned at one end of the lever and the effort at the other end. The load lies somewhere between the fulcrum and effort. Effort is always further from the fulcrum than the load.

Class II Levers

Class III Lever The fulcrum placed at one end of lever but load is furthest from fulcrum. Effort is between the fulcrum and load.

What determines the effects of lever design on lifting power? If a pushing or pulling force is applied at one end of a lever, an action is produced at another point along the lever. The point along the lever at which the effort is applied is just as important as the effort applied.

What determines the effects of lever design on lifting power? 1. When effort is applied further from the fulcrum than the position of the load, less effort is required to raise the load. 2. The effort must move a greater distance to raise the load. 3. Effort distance and load distance depend upon the position of the fulcrum.

What determines the effects of lever design on lifting power? The principle of lever states that the effort multiplied by its distance from the fulcrum is equal to the load multiplied by its distance from the fulcrum.

What determines the effects of lever design on lifting power? 1. Resistance force (resistance distance) = effort force (effort distance) 2. Work=force (distance). The work done at one end of lever equals work done at the other end of the lever. 3. A 100-pound block positioned 2 ft. From fulcrum of a 10-foot lever would require only 25 pounds of effort force. (100(2) = 25(8))

What is the relationship between levers and wheels? Wheels are actually rotating levers. The center of the wheel is the fulcrum. The radius of the wheel is the bar of the lever. The axle rotates a shorter distance than the wheel but has greater force. Turning the wheel causes the wheel to move a greater distance but less force.

How effective are various pulley designs? A pulley is a class I lever. Pulley—A small wheel used to change direction or increase an applied force.

How effective are various pulley designs? A stationary pulley does not offer a mechanical advantage of force. They simply change the direction.

Moveable pulleys multiply effort force. The effort distance is greater and the resistance distance is less. On a single moveable pulley the effort force will be half the load and the effort distance will be twice the load distance.

Multiple pulleys can reduce the effort force required to lift. Multiplication of force is equal to the number of sections of rope that raise the lower set of pulleys attached to a load.

What is the mechanical advantage of an inclined plane? Inclined planes make it possible to move a load with less effort than lifting the load vertically. Inclined plane— Formed by placing a flat surface at an angle to another surface. users.cwnet.com/~thall/bus_ramps.htm

What is the mechanical advantage of an inclined plane? The smaller the slope of the inclined plane, the less effort required to move the load.

What is the mechanical advantage of an inclined plane? To calculate effort forces to move the load remember this formula. Effort force × effort distance = load force × load distance golf-car.com/ramps.htm

Review/Summary What are the classes of levers? What determines the effects of lever design on lifting power? What is the relationship between levers and wheels? How effective are various pulley designs? What is the mechanical advantage of an inclined plane?