Machines
Science: KS3, topic 3.2.22
Machines
Objects that are used to do something such as levers, pulleys and screws are examples of simple machines. A simple machine will multiply a force, which helps us perform a particular function.
Simple machines
- A simple machine makes a job easier for us by reducing the force taken for a job.
- Examples of simple machines include:
- Inclined Planes: A ramp makes it easier for us to move objects higher.
- Wedge: Contains two inclined planes such as the sides of an axe or knife.
- Screw: a screw, drill or screw top lid. These are inclined planes that have been twisted.
- Wheel and Axle: This could be a traditional wheel with a small rod through the middle of it.
- Levers: Use a force to move a load like a door handle, wheelbarrow or light switch.
- Pulley: A rope around a wheel that will move an object up and down.
Gears
- A force multiplier allows us to put a small force in and get a large force out.
- Gears are an example of a force multiplier.
- Gears are an example of a simple machine. A gear is two or more toothed wheels that interlock.
- We use gears on a bike. If you pedal up a mountain, you want a low gear which takes less effort on the first gear.
- This multiplies the force on the interlocking gear, which is bigger, but will not go as far or fast.
Levers
- Levers are simple machines.
- Each lever is made up of 3 parts: The fulcrum or pivot, the effort (input) and the load (output).
- There are three classes of lever.
- Class 1: The fulcrum is placed between the effort and load such as on a seesaw.
- Other examples of a class 1 lever include: a pair of pliers and a trebuchet.
- Class 2 levers: The load is between the fulcrum and effort.
- Examples of class 2 include a nutcracker and wheelbarrow.
- Class 3 levers: The effort is between the fulcrum and load.
- Examples include: Staplers and a person fishing or playing tennis.
Test yourself on Machines
Which of these is not a kind of machine?
Why is a knife classed as a simple machine?
A wheelbarrow is a class 2 lever, with the load between the fulcrum and the effort. Why might this make it easier to lift a heavy load?
A cyclist wants to travel as fast as possible along a flat, easy road. Based on how gears affect force and speed, which gear should they choose?