notes 13-4 machines and the body. force a push or pull on an object described by magnitude...

Notes 13-4

Machines and the body

Force

• A push or pull on an object• Described by magnitude (strength) and

direction• Unit = Newton

Work

• You do work when you exert a force on an object that causes it to move in the same direction as the force

• Work = Force x Distance

• Example: Lifting a box 2 meter using a force of 20 Newtons.

• Work = 20 N x 2 m = 40 Nm

Machines• Machines allow you to do work easier and more

effectively• A lever is a simple machine that makes lifting heavy

objects easier.

Levers

• A lever is a ridged bar that is free to pivot, or rotate, on a fixed point (fulcrum)

Anatomy of the lever

• Fulcrum – point around which the lever rotates• Input Force (Effort Force)– Force exerted ON the

lever• Output Force (Resistance Force) – Force exerted

BY the lever

Levers

• Levers are classified according to the location of the fulcrum relative to the input (effort) and output (resistance) forces.

Mechanical Advantage

• Number of times a lever increases a force exerted on it

• Mechanical Advantage = Resistance ForceEffort

Force

Example: Calculate the mechanical advantage of the lever that’s uses 60 N to move a 120 N box.

MA = 120 N ÷ 60 N = 2 (the lever doubled the effort force)

Levers and the human body

• Your body contains muscles attached to bones in ways that act as levers.

• Here the biceps muscle attached in front of the elbow opposes the muscles in the forearm. Can you think of other muscle

levers in your body?

Simple Machines in the Body• Most of the machines in your body are levers

that consist of bones and muscles.• Joints act as fulcrums, bones acts as levers,

muscles provide the force

Animation on levers

• http://www.s-cool.co.uk/gcse/pe/how-the-body-moves/revise-it/levers

• Video on Levers:• http://www.learn360.com/ShowVideo.aspx?I

D=129086