Work and Simple Machines

What is Work? In science, work includes forces and motion but not concentration. Work The transfer of energy that occurs when a force is applied over a distance Work is done when you apply force Unit of measurement for work is joules (J) Calculating work Can be easily done Formula: W= Fd W: work (joules) F: force (Newtons)

What is Work?: Factors that Affect Work The work done on an object depends on the direction of the force applied and the direction of motion. Force at an Angle: The force and motion aren’t in the same direction Only part of the force does work Example: Suitcase The force will be both horizontal and vertical Only the horizontal force moves the suitcase, and, therefore, it’s the only force that is calculated when calculating work Lifting Objects: Example: Lifting a backpack requires work. Has weight because of gravity pushing down on it Must pull upward with a force that is greater than or equal to the backpack’s weight The work done to lift any object is equal to the weight of the object multiplied by the distance it is lifted

What is Work?

What is Work? Work and Energy Doing work on an object transfers energy to the object Helps in predicting how an object will act when forces are applied to it Kinetic energy Energy that causes an object to move Potential energy Energy at a stand still Example: Lifting an object Increases the object’s energy

What is Power? Doing work does affect power Power The rate at which work is done Unit of measurement for power is Watt (W) Calculating power Formula: P=work/time W: work (joules) T: time (seconds)

What is a Machine? A machine is any device that makes doing work easier. Can range from simple to complex Simple: Snow shovel Complex: Watch All machines make tasks easier, but they don’t decrease the amount of work required. Instead, a machine changes the way in which the work is done.

What is a Machine? Input Force to Output Force Input Work to Output Work Input force The force that you apply to an object Output force The force that the object changes the input force into and puts out Input work Occurs when you apply an input force to a part of the machine Result of the input force and the distance the machine moves in the direction of the input force Output work Converted from input work Occurs when a machine applies the output force on something and making it move The result of the output force and the distance part of the machine moves in the direction of the output force

How do Machines Make Work Easier to Do? Makes work easier three ways by changing the following: The size of a force The distance the force acts The direction of a force

How Do Machines Make Work Easier to Do? Change in the Size of a Force Change the Distance the Force Acts Occurs when the output force is greater than the input force, the output force acts over a shorter distance In other words, a machine makes the work easier by changing the input force into a larger output force Occurs when the output force acts over a longer distance than the input force, the output force is less than the input force In other words, the output force decreases as the distance over which the force acts increases

How Do Machines Make Work Easier to Do? Change the Direction of a Force Equal output and input forces act over equal distances In other words, when the output and input forces are equal, then it can change the direction of the force.

What is Mechanical Advantage? Most machines change the size of the force applied to them. Mechanical advantage The ratio of a machine’s output force produced by the input force applied Tells how many times larger or smaller the output force is than the input force Can be: Less than 1 Equal to 1 Greater than 1 Ideal mechanical advantage can occur if no friction existed Machines can’t operate at ideal mechanical advantage because friction does exist

What is Efficiency? The output work done by a machine never exceeds the input work of the machine Reason is because of friction Friction converts some input work into thermal energy, which can’t be used to do work Efficiency The ratio of a output work to the input work A machine’s efficiency is always less than 100% because the output work is always less than the input work Example: Lubricating a machine’s moving parts increases the efficiency

What is a Simple Machine? A machine that does work using only one movement Six types of Simple Machines: Levers Wheel and axle Inclined plane Wedges Screws Pulleys

Levers Lever A simple machine made up of a bar that pivots or rotates about a fixed point The fixed point is called the fulcrum In levers, the distance from the input force to the fulcrum is known as the input arm In levers, the distance from the fulcrum to output force is known as the output arm Three types of levers: First-class lever Second-class lever Third-class lever

First-Class Levers The fulcrum is between the input force and output force Mechanical advantage for these levers depends on the location of the fulcrum. Greater than 1 The input arm is longer than the output arm Equal to 1 The input and output arms and input and output forces are equal Less than 1 The input arm is shorter than the output arm Examples: Hammer Finger tab on a beverage can

Second-Class Levers The output force is between the input force and fulcrum The output force and input force act in the same direction Makes the output force greater than the input force Mechanical advantage: The input arms are longer than the output arms, causing the mechanical advantage to always be greater than 1. Examples: Wheelbarrow A nut cracker Your foot

Third-Class Levers The input force is between the output force and the fulcrum The output force is less than the input force Both forces act in the same direction Mechanical Advantage: The input arm is always shorter than the output arm, making the mechanical advantage lesser than 1 Examples: Tweezers Rakes Broom

Types of Levers

Levers in the Human Body The human body uses all three classes of levers Examples: Neck First-class lever Fulcrum is the joint connecting the skull to the spine Neck muscles provide input force, and output force helps to support the head’s weight Foot Second-class lever Ball of the foot is the fulcrum Input force comes from the muscles in the calves Arm Third-class lever Elbow is the fulcrum Input forces comes from the muscles located near the elbow

Wheel and axle An axle attached to the center of the wheel and both rotate together Axle can be another word for shaft Example: Screwdriver Steering wheel in a car Mechanical advantage The length of the input arm is the radius of the wheel The length of the output arms is the radius of the axle Help in showing ideal mechanical advantage Mechanical advantage is usually greater than 1 because of the wheel being larger than the axle

Wheel and Axle

Inclined planes A flat, sloped surface Also called a ramp Takes less force using an inclined plane than it does to lift an object straight up Helped the Egyptians in building the pyramids Examples: Wheelchair ramps Ramps used by moving trucks

Wedges A sloped surface that moves A type of inclined plane with one or two sloping sides The shape of a wedge gives the output forces different directions than the input forces Examples: Doorstop Axe Teeth

Screws An inclined plane wrapped around a cylinder When turning a screw, the screw threads change the input force to an output force The output force is what pulls the screw into the material

Pulleys A simple machine that is a grooved wheel with a rope or a cable wrapped around it Can be found in construction sites on the cranes helps to lift heavy loads Fixed pulleys Pulleys that are mounted Only changes the direction of the force Example: Window blinds

Pulleys Moveable pulleys Pulley system Mechanical advantage of pulleys A pulley that can be attached to the object being lifted Decrease the force needed to lift an object Distance over which the force acts increases Pulley system A combination of fixed and moveable pulleys that work together Mechanical advantage of pulleys The ideal mechanical advantage of a pulley and pulley system is equal to the number of sections of rope pulling up on the object

Pulleys

What is a Compound Machine? Two or more machines that operate together is a compound machine Gears Wheel and axle with teeth Two or more gears working together form a compound machine Different sizes helps in turning a different speeds Smaller gears will rotate faster than larger gears The amount of force transmitted through a set of gears is also affected by their size The input force applied to a larger gear can be reduced when applied to a smaller gear Other examples of Compound Machines: Can opener

What is a Compound Machine? Efficiency of Compound Machines: The efficiency is calculated by multiplying the efficiencies of each simply machine together Each simple machine can decrease the overall efficiency of a compound machine