Kinematics in Earth Science -Fagan

From wiki.NGSciEd.org

Original Science Lab

Types of Simple Machines

I have never used a lab of this type since simple machines are not targeted by my set of standards. However, I have explored renewable energy resources in class using solar powered race cars. The sixth grade Earth Science standards due address renewable and nonrenewable energy resources including wind, water and solar.

Science Lab - Water Wheels, Energy Resources and Simple Machines

Grade level targeted:

Sixth Grade Science

GPS Addressed:

S6E6. Students will describe various sources of energy and with their uses and conservation.
S8P3 c. Demonstrate the effect of simple machines (lever, inclined plane, pulley, wedge, screw and wheel / axle) on work.

Background Information:

Machines are tools designed to make our lives easier by reducing the amount of effort required of us or of other parts of the same machine. They are often used to complete jobs faster or reduce the amount of force required to move an object or parts of a machine in a desired direction. Simple machines have been used as early as the axe/wedge and have since become more complicated (pulley systems and wheel/axle) as our need for them has increased.

Every machine require energy to work. The effort, or force required, must be greater than the force resisting the movement of the object. For most machines, the resisting force is either gravity, friction or inertia. The interesting thing about machines is that they can reduce the amount of force required to complete work or even prolong the amount of time that work can be done but the amount of work does not change. Meaning, an axe/wedge might reduce the amount of energy needed to cut a piece of wood but the work required (cutting the piece of wood) does not change.

The mechanical advantage of a machine is the factor by which a machine multiplies the force put into it. Mechanical Advantage (MA) can be found by dividing the output force by the input force (MA=Output Force / Input Force). The higher the MA value (i.e. 1 and above) the more the Input Force is multiplied by the machine, meaning the force applied can be used over a greater distance or for a shorter period of time.

The Ideal Mechanical Advantage (IMA) or Theoretical Mechanical Advantage is the mechanical advantage of an ideal machine (excludes friction, gravity and inertia) for which none exist. The Actual Mechanical Advantage (AMA) of a machine is much more complicated to determine since factors such as friction, gravity and inertia must be considered. A simplified equation for AMA is resistance for divided by actual effort force (AMA = Resistance Force / Force Actual).

The mechanical efficiency of a machine is the difference between the MA and AMA. For example, if the Input Force of 10 Pounds results in an Output Force of 60 pounds then the MA is 6. However, the AMA is less than 6 because some energy is lost to friction, gravity and inertia. The better the mechanical efficiency of a machine the less energy lost between MA and AMA (Wikipedia, Mechanical Advantage).

A simple machine is a mechanical device that changes the direction or magnitude of a force. In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force (Wikipedia, Simple Machines). Types of simple machines include (Edheads):

Gears - Two toothed wheels fit together either directly or through a chain or belt so one wheel will turn the other.
Inclined Plane - A sloping surface, such as a ramp. An inclined plane can be used to alter the effort and distance involved in doing work, such as lifting loads.
Lever - A straight rod or board that pivots on a point known as a fulcrum. The fulcrum can be moved depending on the weight of the object to be lifted or the force you wish to exert.
Pulley - A wheel that usually has a groove around the outside edge. This groove is for a rope or belt to move around the pulley. Pulling down on the rope can lift an object attached to the rope.
Screw - An inclined plane wrapped around a shaft or cylinder. This inclined plane allows the screw to move itself or to move an object or material surrounding it when rotated.
Wedge - Two inclined planes joined back to back. Wedges are used to split things.
Wheel and Axle - A wheel and axle has a larger wheel (or wheels) connected by a smaller cylinder (axle) and is fastened to the wheel so that they turn together.

Integration of Science Concepts - Water Wheels and Water Turbines

Water Wheel and Stamp Mill

The wheel and axle is a lever that turns around a central fulcrum. The outside wheel turns around the center wheel or axle and can be used to accomplish a variety of tasks (such as increasing torque and improving the power in to power out ratio). Types of wheels and axles are screwdrivers, wheels and gears. Another example of a wheel and axle is the water wheel and turbine.

Hydroelectric Dam

The water wheel has been used to run machines before and after the advent of electricity. A water wheel simple turns and axle that is attached to a machine to complete work. The type of work is determined by the need, whether it be grinding grain or turning the gears of machine (stamp mill for breaking down rock).

Water turbines, invented in the 19th century, are primarily used today for electric power generation. The concept is similar to the water wheel but far more efficient for the same size wheel. Water turbines use water to turn a wheel (or turbine) that in the process transfers energy from the water to the wheel that is then harnessed for energy.

Hydropower makes up 67 percent of the renewable energy generated in the United States and 6 percent of the total US energy budget. The amount of available energy in moving water is determined by its flow or fall. Swiftly flowing water in a big river, like the Columbia River that forms the the border between Oregon and Washington, carries a great deal of energy in its flow. Water descending rapidly from a very high point, like Niagara Falls in New York, also has lots of energy in its flow. In either instance, the water flows through a pipe, or penstock, then pushes against and turns blades in a turbine to spin a generator to produce electricity. In a run-of-the-river system, the force of the current applies the needed pressure, while in a storage system, water is accumulated in reservoirs created by dams, then released as needed to generate electricity (Energy Kids).

Management Considerations: Students will be working in groups to build water wheels using K'NEX pieces. Students will also be using water to turn their water wheels. Students should be coached on how to best use the materials used to build their water wheel and be reminded on how to use the sink appropriately.

Common Misconceptions on this Topic

A simple machine with a mechanical advantage greater than one is easier to use than a simple machine with a mechanical advantage less than one.
1. Not all machines yield a MA advantage greater than 1...which is okay. A screwdriver, for instance, does not need to multiple the input force because the operator would damage the screw. Other examples are scissors and fishing rods.
Any force times any distance is work.
1. Since work is a change in kinetic energy, a force will only do work if the force has a component in the direction an object moves.
Machines put out more work than people put in.
1. The amount of work does not change. However, it takes less energy for a machine to complete the same amount of work as a person.
Power is the same as force or work.
1. Power is the rate at which energy is changing form or location. Force is what is causing the change in form or location and work is the application of that force over a distance.
Work is any activity one gets tired doing, gets paid for doing, or doesn’t like doing.
1. I can stand and push on a brick wall all day, get tired, get paid and not enjoy myself but work has not been done since the kinetic energy of the wall has not changed. Bummer.

Inquiry lab instructions

Students will work in groups to design and build a wheel and axle simple machine. Their machine must either lift an object off the ground (cup) or generate electrical energy. A handout will provide instructions for building a water wheel using K'NEX building pieces but students are not restricted to just building a water wheel.

Students will measure the amount of electrical energy generated by their water wheel then modify their water wheel to improve the amount of energy generated. Students can modify the water wheel as needed.

Explanation of how this lab Addresses Identified Misconceptions

A water wheel does not reduce the amount of work needing to be completed but does use a smaller amount of energy to complete the same amount of work. Because of this more work can be completed by the machine than a person could complete in the same amount of time.

Internet Resources:

Wheel and Axle