Mechanical Systems Outcome 2: Structure and Function

Mechanical Systems  How many mechanical systems have you used today?  Examples???  All mechanical systems have an energy source. The energy could come from electricity, gasoline, or solar energy, but often the energy comes from humans.

Mechanical Systems…

Levers and Inclined Planes  Lever: A simple machine that changes the amount of force you need to put on an object to move that object.  It consists of a bar that rotates around a fixed point, the fulcrum.  Effort force: The force you exert on a lever to make it move.

Levers Continued…  Load: The mass of an object that is moved or lifted by a machine such as a lever.  Effort arm: The distance between the fulcrum and the effort force.  Load arm: The distance between the fulcrum and the load.

Lever

Classes of Levers  Class 1 Lever: The fulcrum is between the effort and the load. Scissors

 Class 2 Lever: Always exerts a greater force on the load than the effort force you exert on the lever. The load is between the effort and the fulcrum. Wheelbarrow

 Class 3 Lever: The effort is exerted between the fulcrum and the load. You must put greater force on the lever than the lever exerts on the load. However, the load can be moved very quickly. Hockey stick

Inclined Plane  Inclined Plane: A ramp or a slope that reduces the force you need to exert to lift something.

Wheels, Axles, Gears and Pulleys  You can lift a heavy load as long as you can find a lever that is long enough and strong enough to do the job. Sometimes however it is not practical.  Winch: Consists of a small cylinder and a crank or handle. (A wheel-axle device)  Radius = The distance from the centre of the wheel to the circumference.  The Radius acts like the load arm of a lever.

The Wheel and Axle  Wheel and Axle: Two turning objects are attached to each other at their centers, and one causes the other to turn.

Gears  Gear: A rotating wheel-like object with teeth around its rim.  Gear Train: A group of two or more gears  Driving Gear: First gear, the one in which the initial force is applied.  Driven Gear: Second gear, the one that gets driven

Gears…  Which is the Driving gear?  Which is the Driven gear?  What are gears used in??  Sprocket: A gear with teeth that fit into a chain, like on your bike.

Gears in Contact vs. Sprockets and Chains  Gears in Contact: Turn in opposite directions. Examples?  Sprockets and Chains: Turn in the same direction.

Pulleys  Pulley: A grooved wheel with a rope or chain running along the groove.  Fixed pulley: A pulley that is attached to something that does not move.  Movable pulley: A pulley that is attached to something else, often by a rope that goes around the pulley itself.

More Pulleys  Block and Tackle: A combination of fixed and movable pulleys.  Compound Pulley: Several pulleys working together.

Mechanical Advantage (Pulleys)  Mechanical Advantage: The comparison of the force produced by a machine to the force applied to the machine.  In other words: the comparison of the size of a load to the size of the effort force.  Single Fixed Pulley = MA of 1  Single Movable Pulley = MA of 2  What is the MA of this Pulley?

The Source of Energy! Work is a transfer of energy. You use energy when you push on the pedals of a bicycle and make them move. The pedals now have Kinetic energy.  Kinetic Energy: Energy of motion.  Most of today’s machines are not powered by people. The two main natural resources for energy of machines are fuel, like gasoline, and electrical energy.

Stored Energy  Potential Energy: Stored Energy. Most of the energy for machines, even your body, is stored as chemical energy.  Energy must be transferred to a machine to make the machine work. However, we want to control when the machines work and when they do not. So, we store the energy = potential energy.

Energy Transmitters  Transmission: Energy can be transmitted as well as converted. In transmission, energy can be transferred from one place to another, and no energy is changed or converted.  Example: Electrical wires transmit the power from the generating station to your home.  Examples??