Simple Machines

Goal of the class To investigate the six main types of simple machines To discover how simple machines can apply pushes or pulls (forces) to make things move and how we use them every day Question of the day: By reducing the force to move an object, what becomes greater? The distance you need to move it

Reminder on Work Work is done on an object when a force causes a displacement: W = Fd displacement (metres) work (Joules) force (newtons)

Simple Machines Simple machines can: change the amount of force needed change the distance the force is applied over change the direction of the force. Thus, simple machines increase our mechanical advantage the ability to accomplish work more easily

The Lever A lever consists of a rigid bar that pivots (turns) around a fixed point, the fulcrum Fulcrum

Classes of Lever First Class – Changes the direction of the input force. Example: A seesaw Draw input and output forces Other examples scissors, crowbars, pliers

Classes of Lever Second Class – Increase the force, but don’t change it’s direction Example: A wheelbarrow Draw input and output forces Nutcrackers

Classes of Lever Third Class – Increase the lever’s distance, but don’t change the force’s direction Example: A baseball bat Draw input and output forces Elbow, broom and tweezers

An Inclined Plane An inclined plane consists of a tilted flat surface. The inclined plane allows us to move objects upward more easily than lifting the object directly. Raising an object to a particular height requires a certain amount of work. We cannot change the amount of work needed, but the inclined plane alters how we do the work: it increases the distance over which we do the work, but it decreases the effort needed. Examples of inclined planes include a ramp for loading a truck, a switchback road, and a ladder. Input Force Output Force

Screws Take out a pencil that has a flat side. Make a right-angled triangle from a sheet of paper Wrap the paper around the pencil

Wedges A wedge combines two inclined planes back to back. Wedges move objects apart by being forced under or between them. Wedges change the direction of force applied to them Input Force When you push down on a wedge, the wedge pushes out on the two planes that it is in between. Examples of wedges include axe heads, cutting edges of scissors, points of nails, and door stops. Simple Machines Trivia: The plow, an example of a wedge, was invented in the Middle East in about 3500BC Output Force

Pulleys A pulley is a grooved wheel that spins on a fixed axis with a rope or chain moving over the wheel. They make work easier by changing the direction and amount force needed. Examples of fixed pulleys include flagpoles or miniblinds.

Question of the day Question of the day: If I hold a 10kg box above my head for 15secs how much work is done? The answer is 0J as the box doesn’t move.

Vocabulary Axle - the shaft on which a wheel turns. Fulcrum - the pivot on which a device such as a lever is supported so that it can balance, tilt or swing. Load - the weight of an object that is moved by a machine, or the resistance to movement that a machine has to overcome.

Homework Read pages 114-135 in your textbook (Chapter 4 sections 2 and 3) Mechanical advantage and wheel and axle systems Needed for lab next week