Form 2 Science Chapter 10

Chapter 10: Simple Machine FORM 2

Simple Machine

Levers

Principle of lever Load, fulcrum and force in lever Classes of levers Moments of a force Solve problems related to levers

Design machine to simplify work

•Simple machines are devices that make work easier. •Some of the examples of simple machines are inclined plane, stick, broom, hammer and pulley

•A lever is a simple machine. Hence, levers are used to make work easier.

9.1 Centre of Gravity and Stability

•The diagram below shows a lever.

•A lever is a simple machine which turns about a fixed point called the fulcrum (F) when a force called the effort (E) is applied to overcome a resisting force known as the load (L). •Levers can be classified into three classes based on the relative positions of the fulcrum, the effort and the load. •First-class lever •Second-class lever •Third-class lever

•First-class lever •The fulcrum is between the effort and the load. •Examples are scissors, pliers, see-saw, crowbar and hammer. •Second-class lever •The load is between the fulcrum and the effort. •Examples are wheelbarrow, nutcracker, bottle opener and paper cutter. •Third-class lever •The effort is between the load and the fulcrum. •Examples are ice tongs, fishing rod, broom, stapler and our forearm.

•When we open the door or use a wrench to loosen a nut, we are applying a force that causes a turning effect to accomplish the desired task. •The turning effect is called the moment of a force.

•Moment of a force (Nm)=Force (N) x Perpendicular distance from the fulcrum to the force (m) •Principle of moment •When the lever is in equilibrium, •Load x load distance=effort x effort distance •L x l=E x e •exercise

•We should try to design or improvise a device that uses the principle of lever. •One such example is the barrier placed at the entrance of a parking lot to control cars from entering or leaving the area.

Designing Simple Machines

The end