Whenever you use scissors or use a handle to open a door, you are using a simple machine. Simple machines include levers, ramps, wedges, screws, pulleys, wheels and gears. A force applied over a distance supplies the energy change or work needed to operate the machine. Simple machines can change the size, direction or speed of a force in order to make a job easier.
Machines, energy and force
A simple Machine is a device that makes a job easier to do. A ramp is a simple machine that would help you lift the equipment into the back of the van.
The force you need to apply to get a job done is called effort.
The load is the force actually required to do the job. Simple machines work in three different ways. They can:
- change the size of a force
- make things speed up
- change the direction of a force
Force multipliers
Lifting a car to change a type would require a huge effort. However, a car jack makes the task easier and the effort required smaller. You apply a small force to the handle of the jack, but wind it over a very long distance. This is a type of force multipliers.
Levers
A lever is a simple machine that is made of long, rigid object (such as a stick or a metal rod) and a pivot or fulcrum about which it rotates). Most levers are force multipliers.
When you use a lever as a crowbar, or use a teaspoon to lift a lid from a tin, you are using a first-class lever.
If the load is positioned between the fulcrum and the effort, then the lever is called a second-class lever. This also acts as a force multiplier. A wheelbarrow is an example of such a lever. By lifting the handles a greater distance than the load, the force applied is increased.
Wheels
The center of a wheel is called its axle and the outside of a wheel is its rim. A wheel on an axle is a spectral type of lever. Each spoke of the week is a lever, the axle is the fulcrum and the wheel rim is the outer end of the lever. When you apply a force to turn on a tap, the handle acts as a wheel. It increases the force you apply at its center, allowing the axle to turn.
Gears
Gears are wheels that have teeth around their rim. Gears can mesh directly together, or be joined by a chain, such as bicycle or i the overhead cam shaft in some car engines. A set of geras that are connected is called a gear train. When one gear turns, the gear it interlocks with also turns, but in the opposite direction. The gear that supplies the force is called the driving gear. The gear that is connected to this gear is called the driven gear.
Inclined planes
While levers, wheels and gears can multiply a force to make it larger, ramps or inclined planes are force multipliers that reduce the effort force needed to do a job. Ramps make it easier to shift heavy sound equipment into vans. They also make it easier to climb a mountain. This is why roads wind up mountains. Ramps reduce the effort force required, by making you travel further.
Skews
A skew has a double inclined plane winding around it. The spiral is called the thread. A screw is easy to skew into wood but you need to turn it many times with your skew driver.
Speed Multipliers
A machine can also make something move faster than otherwise possible. You need to apply greater force to these types of machines but the machines speed things up. For this reason they are called speed multipliers.
Tennis racquets, cricket bats and golf clubs are levers that are used as speed multipliers so that they hit balls at high speed. They are examples of third-class levers.
When using a broom, you apply a large effort force to the handle. The handle moves through a much shorter distance than the end of the broom, which moves much faster, but with less force. The broom acts as a third class lever. It has traded increase in force for an increase in speed.
Changing the direction
A machine can also change the direction in which a force acts.
Wedges
Imagine trying to bite into an apple without your front teeth. Your front teeth, called incisors, cut like a knife. These are simple machines called wedges. A wedge is a double inclined plane that moves through another object. Wedges are used to split objects because they change the direction of a force by 90Ëš and increase its size. When an axe is pushed downwards, the wedge of the axe head pushes the wood apart.
Pulleys
Sometimes it is necessary to change the direction of a force. To lift a set of Venetian or Roman blinds, it is much easier to apply downward force on a cable than to try to lift it upwards from a height. A simple way of doing this is to use a pulley.
A pulley is a wheel with a groove around it into which a rope or chain can move. Pulleys can a lot be used as force multipliers if more than a single pulley is used.
