Integrated Science Unit 2, Chapter 4

Unit Two: Work and Energy Chapter 4 Machines and Mechanical Systems 4.1 Force and Machines 4.2 The Lever 4.3 Gears and Design

Chapter 4 Learning Goals Describe and explain a simple machine. Apply the concepts of input force and output force to any machine. Determine the mechanical advantage of a machine. Construct and analyze a block and tackle machine. Describe the difference between science and engineering. Understand and apply the engineering cycle to the development of an invention or product. Describe the purpose and construction of a prototype. Design and analyze a lever. Calculate the mechanical advantage of a lever. Recognize the three classes of levers. Build machines with gears and deduce the rule for how pairs of gears turn. Design and build a gear machine that solves a specific problem.

Chapter 4 Vocabulary Terms engineering gear engineering cycle engineers force fulcrum gear input input arm input force input gear lever machine mechanical advantage mechanical systems output output arm output force output gear prototype simple machine

4.1 Forces in Machines Key Question: How do simple machines work?

4.1 Forces in Machines A machine is a device with moving parts that work together to accomplish a task. Machines are designed to do something useful.

4.1 Forces in Machines You can think of a machine as having an input and an output. The input includes everything you do to make the machine work. The output is what the machine does for you.

4.1 Forces in Machines A simple machine is an unpowered mechanical device, such as a lever. A lever allows you to move a rock that weighs 10 times as much as you do (or more). Some other important simple machines are the wheel and axle, the block and tackle, the gear, and the ramp.

4.1 Forces in Machines Simple machines work by manipulating forces. It is useful to think in terms of an input force and an output force.

4.1 Mechanical Advantage MA = Fo Fi Output force (N) mechanical Input force (N)

4.1 Mini Quiz What is a machine? What do input and output mean? Name five simple machines ? What is mechanical advantage? Why is the block and tackle such an extremely useful machine?

4.2 The Lever Key Question: How does a lever work?

4.2 The Lever A lever includes a stiff structure (the lever) that rotates around a fixed point called the fulcrum. The side of the lever where the input force is applied is called the input arm. The output arm is the end of the lever that moves the rock or lifts the heavy weight.

4.2 The Lever

4.2 Mini Quiz What are the parts of a lever? What do you calculate the mechanical advantage of a lever? Describe a 1st class lever. Describe a 2nd class lever. Describe a 3rd class lever.

4.3 Gears and Design Key Question: How do gears work?

4.3 Designing Gear Machines The application of science to solve problems is called engineering or technology. People who design technology to solve problems are called engineers.

4.3 Designing Gear Machines Suppose you are assigned to build a bridge that will hold a brick without breaking. Your structure is a truss because you have seen bridges that use trusses. Your idea is called a conceptual design. Your next step is to build a prototype and test it. Good engineers often build many prototypes and keep testing them until they are successful under a wide range of conditions. The process of design, prototype, test, and evaluate is the engineering cycle.

4.3 Gears Gears are better than wheels because they have teeth and don’t slip as they turn together. Two gears with their teeth engaged act like two touching wheels with the same diameters as the pitch diameters of the gears .

4.3 Gears The rule for how gears turn depends on the number of teeth in the gears. The input gear is the one you turn, or apply forces to. The output gear is the one that is connected to the output of the machine. The gear ratio is the ratio of output turns to input turns.

4.3 Gear Ratios To = Ni Ti No Number of teeth on input gear Turns of output gear To = Ni Ti No Turns of input gear Number of teeth on input gear

Machines

4.3 Mini Quiz What is technology? What do engineers do? Describe the engineering cycle. Why are gears better than wheels? What is the gear ratio?