Force & Simple Machines (Part 2) Important Notes - Class 5 Science - Complete Learning Material PDF

Machines

Tools and devices that make our work easier by reducing the force required or the time taken to do a task are called machines. Machines help us perform tasks more comfortably and efficiently.

• Machines help us do work with less effort.
• Machines help us do work in less time.
• Machines make daily life easier and more comfortable.

Simple and Complex Machines

Machines may be simple or complex.

• Simple machines are tools with a very simple structure that make work easier and faster by changing the direction or magnitude of a force, or by increasing distance moved.
• Complex machines consist of two or more simple machines combined to perform a task. Examples include bicycles, cars and sewing machines where several simple machines work together.

Types of Simple Machines

There are six common types of simple machines. Each type changes the way force is applied so that we can do work more easily.

1. Lever

A lever is a rigid rod that can turn around a fixed point. A lever has three important parts:

• Fulcrum: the fixed point about which the lever turns.
• Load: the object or resistance on which work is done.
• Effort: the force applied to move the load.

Depending on the relative positions of the fulcrum, load and effort, levers are classified into three classes.

• Class 1 lever: The fulcrum is between the load and the effort. This arrangement can either increase force or increase distance moved depending on the distances from the fulcrum.
  Examples: see-saw, scissors, crowbar, pliers.

• Class 2 lever: The load is between the fulcrum and the effort. This arrangement always increases the force applied (mechanical advantage > 1), so less effort is needed to lift a heavy load. 
  Examples: wheelbarrow, bottle opener, nutcracker.

• Class 3 lever: The effort is between the fulcrum and the load. This arrangement increases the distance and speed of the load but requires a larger effort than the load (mechanical advantage < 1). Class 3 levers are used where speed or precision of movement is needed rather than force amplification.
   Examples: tweezers, fishing rods, tongs, some types of staplers.

2. Wheel and Axle

A wheel and axle is a simple machine made of a larger wheel fixed to a smaller rod called axle so that both turn together.

• The wheel and axle make it easier to move or turn objects by allowing force to be applied at the rim of the wheel or at the axle.
• Examples: steering wheel of a car, doorknob, screwdriver, some parts of sewing machines.
• There are two basic ways to use a wheel and axle:
• The force can be applied to the wheel so that the axle turns.
• The force can be applied to the axle so that the wheel turns.

3. Inclined Plane

• An inclined plane is a flat surface set at an angle (a slope) so that one end is higher than the other.
• Using an inclined plane reduces the effort needed to raise an object by allowing the object to be moved over a longer distance instead of lifting straight up.
•  An inclined plane makes it easier to push up a load.
• Examples: ramps used to load goods onto trucks, staircases, slides, and sloping roads in hilly areas.

Practical note: an inclined plane gives a mechanical advantage because a smaller force applied over a greater distance can raise the same load.

4. Wedge

• A wedge is formed when two inclined planes are joined back to back in a V shape, or it can be any object with a sharp, sloping edge.
• Wedges convert a force applied to their blunt end into forces that push material apart at their sharp edge.
• Examples: a knife, an axe, a chisel, and the point of a nail are all wedges used to cut, split or hold materials apart.

5. Screw

• A screw looks like a nail with grooves cut in it. 
• A screw is like an inclined plane wrapped around a cylinder. The spiralling ridge on a screw is called its thread.
• To insert it into wood, it has to be screwed in by turning it round and round with a screwdriver.
• Compared with driving a nail, inserting a screw into wood usually requires less direct pushing force but more turns (distance), so a screw provides mechanical advantage.
• Examples: bolts and nuts, screw jacks (used to lift cars), and many fastening screws in furniture.

6. Pulley

A pulley is a wheel with a grooved rim through which a rope or chain passes. Pulleys are used to change the direction of a force .

• Fixed pulley: The axle of the pulley is fixed to a support. A fixed pulley changes the direction of the force but does not reduce the effort needed. Examples: drawing water from a well, raising a flag on a flagpole.

• Movable pulley: The pulley moves with the load. A movable pulley reduces the effort needed to lift a load because it shares the load between rope segments. Movable pulleys are often used together with fixed pulleys in a block-and-tackle arrangement to lift heavy objects.

Using several pulleys together can greatly reduce the force required to lift heavy loads, though the rope must be pulled through a greater distance.

Safety Habits While Using Simple Machines

Simple machines help us, but they must be used safely to prevent injury and damage.

• Moving parts of pulleys, levers and other machines can cause serious injuries; always keep hands and loose clothing away from moving parts.
• Do not stand or work under heavy loads being lifted by pulleys or cranes; stay clear of the lifting area.
• Check ropes, chains and supports for wear or damage before using a pulley. Replace worn parts promptly.
• Keep machines well lubricated and in good repair to avoid sudden failures.
• Sharp edges of knives, scissors and axes are dangerous; handle them carefully and pass them point-first if handing them to someone else.
• Do not wave scissors or other sharp tools around; hold them by the handle and keep blades closed when not in use.
• When carrying sharp or pointed tools, point the sharp end downward and away from your body and others.
• Store sharp and pointed tools in a toolbox or sheath to protect both people and the tools.
• Do not leave tools such as hoes or axes leaning where they can fall or cause someone to trip; store them safely on stable ground or hang them securely.