Lesson Notes By Weeks and Term v5 - Grade 10
Simple mechanisms and mechanical advantage – Week 8 focus
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Simple mechanisms and mechanical advantage – Week 8 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Mechanical Technology
Class: Grade 10
Term: 2nd Term
Week: 8
Theme: General lesson support
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Simple mechanisms are the fundamental building blocks of more complex machines. Understanding them is crucial for anyone interested in how things work, from fixing a bicycle to designing a new piece of agricultural machinery. In South Africa, where many communities rely on ingenuity and resourcefulness to solve everyday problems, understanding simple mechanisms provides valuable skills for maintenance, repair, and even innovation.
Furthermore, a grasp of mechanical advantage allows us to do more work with less effort, something particularly important where physical labour is prevalent. This knowledge is also foundational for future studies in engineering and related fields.
What are Simple Machines? Simple machines are basic mechanical devices that change the direction or magnitude of a force, making work easier. They don't reduce the amount of work done, but they do reduce the amount of force required to do the same work.
There are six fundamental types: Lever: A rigid bar that pivots around a fixed point called a fulcrum. Levers are classified into three classes depending on the relative positions of the fulcrum, the load (resistance), and the effort (force).
Examples: crowbar, see-saw, bottle opener.
Wheel and Axle: A wheel attached to a smaller axle. The force applied to the wheel is amplified at the axle.
Examples: steering wheel, screwdriver, door knob.
Pulley: A grooved wheel with a rope or cable that runs around it. Pulleys can change the direction of force or provide mechanical advantage.
Examples: flagpole pulley, crane pulley.
Inclined Plane: A sloping surface used to raise or lower objects. The force required is less than lifting the object vertically, but the distance is greater.
Examples: ramp, stairs.
Wedge: A double inclined plane used to separate or split objects.
Examples: axe, knife, nail.
Screw: An inclined plane wrapped around a cylinder. Converts rotational motion into linear motion.
Examples: screw, bolt.
Mechanical Advantage (MA): Mechanical advantage is the ratio of the load (resistance force) to the effort (applied force). It indicates how much a machine multiplies the force you apply. MA = Load / Effort A mechanical advantage greater than 1 means the machine multiplies the force (less effort is needed). A mechanical advantage less than 1 means the machine reduces the force, but increases the distance over which the force is applied.
Velocity Ratio (VR): Velocity ratio is the ratio of the distance the effort moves to the distance the load moves. It's a theoretical value based on the geometry of the machine. VR = Distance moved by Effort / Distance moved by Load Efficiency: Efficiency is the ratio of the work output to the work input. It accounts for energy losses due to friction. Efficiency = (Work Output / Work Input) x 100% = (MA / VR) x 100% No machine is 100% efficient due to friction.
Work: Work is done when a force causes an object to move a certain distance. Work = Force x Distance
Example 1: Lever
A builder uses a crowbar (lever) to lift a concrete slab. The fulcrum is placed 0.2 meters from the slab. The builder applies a force of 200 N at a distance of 1 meter from the fulcrum.
a) Calculate the mechanical advantage.
b) Calculate the load (weight of the slab) that can be lifted.
Solution: