Transcript machine - My CCSD

What is a machine?
A machine is a device that makes work easier by changing
1. the amount of force you exert,
2. the distance over which you exert your force, or
3. 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.
Output
distance
Ideal mechanical = Distance from fulcrum to input force
advantage
Distance from fulcrum to output force.
Input
distance
st
1
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).
rd
3
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.