Essential Questions

Why do we use simple machines? Why is mechanical advantage

important? How do different pulley designs alter the

mechanical advantage? How can simple machines work together to

perform a task?

The 6 Simple Machines

Inclined Planes The inclined plane is a

plane surface set at an angle, other than a right angle, against a horizontal surface. The inclined plane permits one to overcome a large resistance by applying a relatively small force through a longer distance than the load is to be raised. Examples: ramps,

sloping road, chisels, hatchets, plows, and carpenter’s planes

Inclined Plane Mechanical Advantage – the wedge splits the force into two smaller

forces – one perpendicular and one parallel to the plane.

The ratio of the triangle's height to its hypotenuse determines how much effort the man must exert to move the cylinder up the plane at a uniform speed.

○ 1 Man pushing a cylinder up a smooth inclined plane. The cylinder weighs 60 pounds.

○ GIVEN #1: Distance rolled = 2 feet to a height of 1 foot. EFFORT = 30 pounds or 1/2 of 60.

○ GIVEN #2: Distance rolled = 3 feet to a height of 1 foot. EFFORT = 20 pounds or 1/3 of 60.

○ GIVEN #3: Distance rolled = 4 feet to a height of 1 foot. EFFORT = 15 pounds or 1/4 of 60.

The Wedge A wedge converts motion in one direction into a splitting motion that acts at

right angles to the blade. Nearly all cutting machines use the wedge. A lifting machine may use a wedge to get under a load.

The Screw This simple machine is a modification of the wedge

designed to yield a very large mechanical advantage in minimum space. The screw is essentially a transfer device of motion and/or force.

The screw can function in two principle ways: It can raise weights and it can press or fasten objects! In the

former role, it converts rotary motion into straight line motion.

It was first used a fastener by ancient goldsmiths for locking bracelets.

A screw finds its mechanical advantage in the ratio of two dimensions: the length of the lever that turns it and the distance between threads ( or its pitch ).

The Screw This simple demonstration shows how a screw is

actually an inclined plane. Materials

Pencil Paper Colored felt tip marker Scissors

Procedure Cut a right triangle from the paper. The dimensions should

be about 5 inches, by 9 inches, by 10.3 inches. Use the felt tip marker to color the longest edge (10.3

inches) of the triangle. Position the shortest side (5 inches) of the triangle along

the side of the pencil and then evenly wrap the paper around the pencil by rolling the pencil.

Activity from: Resources for Science Learning – the Franklin Institute

A Lever

A lever is an arm that "pivots" (or turns) against a "fulcrum" (or point). Think of the claw end of a hammer that you use to pry nails loose. It's a lever. It's a curved arm that rests against a point on a surface. As you rotate the curved arm, it pries the nail loose from the surface.

The Wheel Another kind of lever, the wheel

and axle, moves objects across distances. The wheel, the round end, turns the axle, the cylindrical post, causing movement. On a wagon, for example, the bucket

rests on top of the axle. As the wheel rotates the axle, the wagon moves.

Imagine placing your pet dog in the bucket, and you can easily move him around the yard.

The Pulley Instead of an axle, the wheel could also

rotate a rope or cord. This variation of the wheel and axle is the pulley.

In a pulley, a cord wraps around a wheel. As the wheel rotates, the cord moves in either direction. Now, attach a hook to the cord, and you can use the wheel's rotation to raise and lower objects. On a flagpole, for example, a rope is attached

to a pulley. On the rope, there are usually two hooks. The cord rotates around the pulley and lowers the hooks where you can attach the flag. Then, rotate the cord and the flag raises high on the pole.

Compound Machines

If two or more simple machines work together as one, they form a compound machine. Most of the machines we use today are compound machines, created by combining several simple machines.

Mechanical Advantage

View the following Youtube video to learn about Mechanical Advantage.

http://www.youtube.com/watch?v=yfAdmRJDKIc

Mechanical Advantage = output force/input force

Pulley Lab

Complete the Pulley Lab to examine how mechanical advantage is calculated and which pulley systems are more effective.