Work What is work? –Work is what happens when a force moves an object over a distance in the direction of the force. –Examples: Push a shopping cart Turn a doorknob Kick a ball Lift a box

Work Formula *The unit for work is the Joule. *One joule is equal to one newton-meter.

Let’s Try It Suppose you need to use a constant 100 Newtons of force to push a crate 12 meters. How much work would you do? –W = Fd –W = 100N X 12m –W = 1200Nm AKA 1200J –By using a simple machine, the same job might require only a 75N force.

Simple Machines What is a simple machine? –A device that makes work easier by changing the size, direction, or both size and direction of the force used to do the work. –It does not help you do LESS work! –It just makes the work easier for you to accomplish!

Types of Simple Machines

Inclined Planes A straight, slanted surface that does not move. Example: ramp It is easier to push an object up a ramp than it is to lift the same object straight up to the same height. Increasing the distance decreases the force (effort) needed to do the same amount of work!

Wedges A wedge is two inclined planes placed back-to-back to form a sharp edge. A wedge is used to increase force. Examples: knife, hatchet, axe Used to split things apart.

Screw A screw is an inclined plane that is wrapped around a cylinder. A screw will change the force you use to an output force doing work. The friction between the threads of a screw and the material hold the screw in place. Click here to watch video

Levers A lever is a simple machine made up of: 1.a bar that pivots at a fixed point called a fulcrum. 2. The force applied to a lever called the effort. 3. The object moved is the load. Click here to watch video

3 Types of Levers 1 st class lever = the fulcrum is located between the effort and the load. –Examples: see saw, shovel

3 Types of Levers 2 nd class = the load is located between the fulcrum and the effort. –Examples: wheelbarrow, nutcracker

3 Types of Levers 3 rd class = the effort is applied between the fulcrum and the load –Example: your arm, broom

Wheel and Axles A simple machine that consists of two circular objects of different sizes. The wheel is always larger than the axle. When effort is applied to move the wheel, the axle turns a shorter distance but moves with more force. Example: doorknob, gears

Pulleys A pulley consists of a rope or chain wrapped around a wheel. A load is attached to one end of the rope. A force is applied to the other end of the rope. Pulleys can be fixed or moveable. Pulleys are set up in different ways depending on the work that needs to be done. Click here to watch the video

Compound Machines Most of the objects that we call “machines” are actually compound machines…. meaning that they are made up of two or more simple machines. A compound machine is a system = a group of parts that work together.

Example of Compound Machines Scissors

Mechanical Advantage A calculation of how much a machine multiplies force. The input force, usually given in Newtons, is the force applied by the user on the machine. The output force is the force applied by the machine to the object being worked on.

MA Formula Mechanical Advantage = output force input force Suppose a student uses a force of 30N to push a 300Nbox up a long ramp onto a platform. What is the MA of the ramp? MA = 300N / 30N MA = 10 Means that the ramp multiplies the student’s input force 10 times as it is used to do work!

Friction When a machine is used to do work, some of the input work is “lost” due to friction (the force that acts between surfaces that touch each other). So…the amount of work put into a system is always greater than the amount of work that is done to the actual object. Friction tends to oppose motion. Machines must overcome the force of friction in order to do work. If the object does not move then NO work is done!!