Work • Work = force x distance. • Unit for force is a newton. • Unit for work is a joule.
Lever parts: • Where these things are will determine what type of lever it is. • Fulcrum – pivot point that is attached to lever • Load (resistance arm) • Effort arm (force)
1st class levers • Fulcrum is in the middle. • Load is on one end and the effort arm is on the opposite end. • Examples include: see-saws, some tongs, & crow bars.
2nd class levers • Load is in the middle. • Fulcrum is on one end and the effort arm is on the other. • Examples include: wheelbarrows & nutcrackers.
3rd class levers • Effort arm is in the middle. • Fulcrum is on one end. • Load is on the other. • Examples include: fishing poles, your arm when you are holding something, a rake, and tweezers.
Pulleys: 1st class levers • Defined as a wheel with a groove along its edge. • Pulley pivot is fulcrum. • One end of rope is the effort arm and the other end holds the load. • More pulleys mean force required will be decreased.
Wheel and axle: another lever • Fulcrum is the center part of the wheel. • The effort arm is the radius of the wheel. • The load is carried on the radius of the axle.
Inclined Planes • An inclined plane is a flat sloping surface. • Examples include: ramps, slides, & roads on a hillside.
Wedges • Wedges are 2 inclined planes put together. • Examples include: wood wedges, mauls, axes, knives, and needles.
Screws • A screw is an inclined plane wrapped around a cylinder. • How is a screw different from a nail?
Archimedes screw is a spiral screw turnedinside a cylinder. It was invented in the 3rd century B.C. and was used to lift water from canals. The screw is still used today to lift water in the Nile delta in Egypt, and is often used to shift grain in mills and powders in factories.
Compound machines • Made up of 2 or more simple machines. • Examples include a pencil sharpener, scissors, & a tape dispenser.
Efficiency • Defined as ratio of work that comes out of a machine to the work put into a machine. Ratios can be expressed as 50:25 or 50/25. • The higher the percent, the greater the machine’s efficiency (or the less work the machine wastes).
Friction • A force that opposes motion whenever 2 surfaces rub together. • Friction reducers include oil & ball bearings. • Reducing friction makes machines more efficient.