Presentation on theme: "LEVERS. What is a lever? The lever is a very simple and common machine that can be used to reduce the effort that is needed to get a job done. A lever."— Presentation transcript:
What is a lever? The lever is a very simple and common machine that can be used to reduce the effort that is needed to get a job done. A lever is usually a long, rigid object that moves around a turning point called a fulcrum or pivot. You need to put in an effort to make the lever move a load. Levers are named according to where the fulcrum, load and effort are positioned along the lever. There are three types of levers: First class levers Second class levers Third class levers
What do levers do? All levers are either force multipliers or speed multipliers. Force multiplying levers Multiply the effort you use. This means that you may be able to move loads that you couldn’t move without the lever. Speed multipliers Increase the speed of an object. A big effort needs to be applied, but the load moves over a greater distance, at a higher speed.
First-Class Levers First-class levers turn around a fulcrum that is between the effort and the load. First-class levers are force multipliers. Examples include: seesaw shoehorn wheel and axle - because the wheel's motions follows the fulcrum, load arm, and effort arm principle. chopsticks with hand - the middle finger acts as a pivot.
First-class levers in your body Nod your head Pivot is the place where your skull meets the top of your spine. Skull is the lever arm and the neck muscles at the back of the skull provide the force (effort) to lift your head up against the weight of the head (load). When the neck muscles relax, your head nods forward.
Second-Class Levers Second-class levers turn around a fulcrum that is at the end of the lever. Second-class levers are force multipliers. The load is always between the effort and the fulcrum. Examples include: bottle opener springboard wheelbarrow wrench nutcracker oar - the water is the fulcrum; the boat is the load and the effort is at the inboard end
Second-class levers in your body Stand on tip toes The pivot is at your toe joints and your foot acts as a lever arm. Your calf muscles and Achilles tendon provide the effort when the calf muscle contracts. The load is your body weight and is lifted by the effort. The effort force needed is less than the load force, so there is a mechanical advantage. This muscular movement at the back of your legs allows you to move your whole body a small distance.
Third-Class Levers Third-class levers are those in which the effort is between the fulcrum and the load. Third-class levers are speed multipliers. Examples include: tennis racquet tongs hammer broom fishing rod spring-loaded mousetrap leg when kicking football
Third-class levers in your body Bend your arm The pivot is at the elbow and the forearm acts as the lever arm. The biceps muscle provides the effort (force) and bends the forearm against the weight of the forearm and any weight that the hand might be holding. There is no mechanical advantage because the effort is greater than the load. However this disadvantage is compensated with a larger movement – a small contraction of the biceps produces a large movement of the forearm. This type of lever system also gives us the advantage of a much greater speed of movement. Many muscle and bone combinations in our bodies are of the Class 3 lever type.
Mechanical Advantage Mechanical advantage measures how much easier a lever makes a task. Mechanical advantage load effort For a first class lever, placing the fulcrum closer to the load means that less effort can be exerted to move a heavier load. This means the lever will have a greater mechanical advantage. =
Levers in Everyday Life –Goldfields Windlasses used a wheel and axle (first class lever) to wind buckets of rock and soil to top of the mining shaft. The miner at the top turned the handle (the wheel) and the rope wound around the axle, raising the bucket. Whips were simple first-class levers used to lift buckets of rock and soil to the top the mining shaft. Longer handles made lifting easier.
Levers in Everyday Life – Building Sites Hammer removing nail is a first-class lever Wheel-barrow handles are a second- class levers Screwdrivers are simple wheel and axles (first-class lever)
Levers in Everyday Life - Kitchen Using a spoon to open milo can is using it as a first-class lever Wheel and axle combinations include taps (force multiplier) and ceiling fans (speed multipliers) Hinges on cupboards are second-class levers
Levers in Everyday Life - Sport Tennis racquets, cricket bats and softball bats are all third-class levers - they make objects move faster and further. Rowing – the oar acts as a second class lever. Diving – the springboard acts as a second class lever.