What is a machine? A machine is a device that makes work easier by changing the amount of force you exert, the distance over which you exert your force, or the direction in which you exert your force.

Work In, Work Out When you use a machine you do work on the machine (input or effort force), and the machine does work on something else (output or resistance force).

Machines do not save work! Remember: Work = Force x Distance

When a machine changes the size of the force, the distance through which the force is exerted must also change.

Work input Machine Work output Example:

Work input Machine Work output Example:

Work input Machine Work output Example:

Window blinds do not multiply force, they change the direction of the effort force. Pulling down on the cord changes the direction of the force to pull the blinds up. Effort force and resistance force are equal. Mechanical advantage is 1

What is Mechanical Advantage? Mechanical advantage is a number that tells how many times a machine multiplies force. Mechanical advantage (MA) = output force (Resistance) input force (Effort)

MA = 500 N = 10 50 N

What is a lever? A lever is a rigid bar that is free to pivot, or rotate, about a fixed point (fulcrum).

First class levers Can be used to increase force or to increase distance.

Second class levers Second class levers do not change the direction of the input force, but allow you to apply less force than the force exerted by the load.

Third class levers Do not change the direction of the input force and do not increase the input force. Output force is always less than the input force.

Mechanical Advantage of levers. Ideal mechanical = Distance from fulcrum to input force advantage Distance from fulcrum to output force.

1st Class Levers Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged. For the Class 1 lever the pivot lies between the effort and load. A see saw in a playground is an example of a Class 1 lever where the effort balances the load. This pivot exists in the place where your skull meets the top of your spine. Your 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. http://www.sciencelearn.org.nz/contexts/sporting_edge/sci_media/images/tip_toe

2nd Class Lever Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged. For the Class 2 lever the load is between the pivot and the effort (like a wheelbarrow). The effort force needed is less than the load force, so there is a mechanical advantage. Standing on tip toes is a Class 2 lever. 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 (muscle contraction).

3rd Class Lever Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged. For a Class 3 lever the load is further away from the pivot than the effort. There is no mechanical advantage because the effort is greater than the load. However this disadvantage is compensated with a larger movement. This type of lever system also gives us the advantage of a much greater speed of movement. A bent arm is a Class 3 lever. 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.

Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged. For a Class 1 lever the pivot lies between the effort and the load. A see saw in a playground is an example of a Class 1 lever where the effort balances the load. The place where your skull meets the top of your spine is a Class 1 lever. Your 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.

Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged. For the Class 2 lever the load is between the pivot and the effort (like a wheelbarrow). The effort force needed is less than the load force, so there is a mechanical advantage. Standing on tip toes is a Class 2 lever. 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 (muscle contraction).

Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged. For a Class 3 lever the load is further away from the pivot than the effort. There is no mechanical advantage because the effort is greater than the load. However this disadvantage is compensated with a larger movement. This type of lever system also gives us the advantage of a much greater speed of movement. A bent arm is a Class 3 lever. 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.