Science ch 6 Work and Machines

Screw

A simple machine that consists of an inclined plane wrapped around a cylinder or cone.

Wedge

A simple machine that consists of two inclined planes, but unlike one inclined plane, a wedge only works when it moves.

Inclined Plane

A simple Machine consisting of a sloping surface that connects lower and higher elevations.

Wheel and Axle

A simple Machine that consists of two connected rings or cylinders, one inside the other, which both run in the same direction around a single center point.

Lever

A simple machine consisting of a bar that rotates around a fixed point called the fulcrum. There are three classes, the first, in which the fulcrum is in the middle, the second class, which the fulcrum is one one end carrying the heavier object (wheelbarrow) and the third class, in which the fulcrum is on the other end, carrying the lighter object.

Pulley

A simple machine that consists of a rope and a grooved wheel.

Why can't you get more work out of a machine than you put into it?

All machines must use some of the work put into them to overcome friction. The amount of work depends on the efficiency of the machine.

Give on example of a machine that changes the direction of a force.

Changing Direction - (flagpole rope system) the direction of the force applied by the user is reversed by the machine.

What is the formula for determining Ideal Mechanical Advantage?

Ideal mechanical Advantage = input force/ output force

Explain how a machine makes work easier.

Machines make work easier by increasing the amount of force that is applied, increasing the distance over which the force is applied, or changing the direction in which the force is applied.

What is Ideal Mechanical Advantage?

The ideal mechanical advantage represents the multiplication of input force that would be achieved in the absence of friction.

Formula for calculating work.

Work = force x distance

What two things do you need to know in order to calculate mechanical efficiency?

You need to know the output work and the input work.

Power

measure of the amount of work that can be done in given amount of time.

Machine

A machine is any device that makes work easier by changing a force.

What formula is used to determine mechanical efficiency?

Efficiency = output work/ input work x 100%

What are the two things that must happen for work to be done?

For work to be done, the force must be applied in the same direction that the object moves. If a force is applied in different direction than the object moves, no work is done.

Give one example of a machine that changes the distance of a force.

Increasing Distance - (paddles) the machine increases the distance over which the force is applied, but it reduces the strength of the applied force.

Give one example of a machine that increases the force.

Increasing Force - (doorknob) the force applied by the user is less than the force applied by the machine, but the machine applies the force over a shorter distance.

Define: Mechanical advantage

Is the number of times a machine multiplies the input work.

Define: Mechanical efficiency

Is the percent of input work that becomes output work. It is a measure of how well a machine reduces friction.

How does reducing friction increase the mechanical efficiency of a compound machine?

Less work has to be done to overcome the force.

What is the formula for determining Mechanical Advantage?

MA = output force/ input force.

Formula for determining power

Power = work/time

Watt

SI unit for power. A watt equals 1 joule of work per second.

Joule

SI unit for work. One joule equals the amount of work that is done when 1 newton of force moves an object over a distance of 1 meter.

Work

The use of force to move an object.