Machines Make Work Easier
Speed Ratio
Speed ratio looks at how the speed of an object is affected by a machine.
|
SR = distance (input)
distance (output) |
Friction & Efficiency
The Science of Work
When we think of work, we think about studying really hard, or doing chores around the house. We may even think about trying to lift a really heavy object and even when we aren't successful, we think we've done a lot of hard work.
This is NOT the case. The scientific definition of work states that, when a force is applied to an object which in turn causes that object to move, work is being done. No movement = No work being done! |
|
We can calculate how much work is being done by comparing the amount of force required to move an object a specific distance. This is represented in the following formula:
W = F x d Work is always measured in Joules. An English scientist, James Joule, was especially interested in the relationship between work and energy. |
Hydraulics
Most machines that move very large objects use a hydraulic system that applies force to levers or gears. A hydraulic system increases the mechanical advantage of the levers in machines.
A hydraulic system uses a liquid under pressure to move loads. Hydraulic systems work because they use fluids under pressure. Pressure is a measure of the amount of force applied to a given area: P = F A |
Section Review
- Define the following: Mechanical Advantage, Speed Ratio, Work, Pressure, Hydraulics, Effectiveness, Function, Design
- Calculate the MA of the following machines:
- Calculate the SR of the following machines:
- How do MA and SR, combined with friction, impact the efficiency of a machine. Use detail in your response.
- How much work is being done if a person rolls a 25000g ball up a ramp that is 5m long?
- A piston has an area of 3cm2, and is pushed down with a force of 5N. What is the area of the output piston if it moves with a force of 27N? How much pressure is exerted within the system?
- Identify 3 factors that can influence the development of a new mechanical device.
- Explain the difference between function and the design of a device. What measurements and observations could you make about a mechanical device in order to determine if it functions well?
- Think of an example through history where trial and error may have been used to develop a device. Explain the trials.
- Is there a difference between efficiency and effectiveness? Use an example as part of your explanation.
- What are the criteria you can use to evaluate a machine. Use an example as part of your explanation.