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# Chapter 2.1.1 Work in Mechanical Systems PowerPoint PPT Presentation

Chapter 2.1.1 Work in Mechanical Systems. Principles of Technology I Edinburg North High School. Notes 2.1.1 Work in Mechanical Systems. Objectives: Define work done by force or torque in a mechanical system.

Chapter 2.1.1 Work in Mechanical Systems

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## Chapter 2.1.1Work in Mechanical Systems

Principles of Technology I

Edinburg North High School

### Notes 2.1.1Work in Mechanical Systems

Objectives:

• Define work done by force or torque in a mechanical system.

• Explain the relationship between work, force applied, and the distance an object moves.

• Solve problems, given force and distance information in English and SI units.

### Work in Mechanical Systems

• Work is done when a force moves an object through a distance (Fig. 2.1).

• Chain hoist

• Gears

• We will see that with rotating systems it will be easier to calculate Wwith 

### Work Done by a Force

• Work – a quantity equal to the product of the applied force and the distance though which the object moves.

• What are the units for work?

• The distance and direction through which an object moves is called displacement.

• Work is the product of two vector quantities:

• In this chapter we will only consider work in one dimension.

• If F and d are in the same direction – positive work

• If F and d are in opposite directions – negative work

### Example 2.1 Work Done by A Weight Lifter (p.85)

• Calculate the amount of work done by a weight lifter in lifting a 200 lb barbell a distance of 5 ft.

• A closer look at lifting a barbell (Fig. 2.2)

• Initial force to get barbell moving, a bit stronger

• As barbell moves at a constant speed

• At highest point, and held in place, no work is being done even though

• You feel tired because work is still being done by your muscles.

### Example 2.2. Work Done to Stop a Trailer

• A car and trailer are moving to the right. The driver applies the brakes and stops the car in 5 m. A constant braking force of 900 N is applied over this distance. What is the direction of the braking force? How much work is done on the car by this force?

• Work is done only while the force is being applied.

### Work Can Change an Object’s Potential Energy or Kinetic Energy

• In general, the work done on an object equals to the objects change in energy state.

• In Example 2.1

• In Example 2.2

### Sample Problem A

• A 2 kg object is lifted onto a table 1.5 m high. Calculate the work necessary to move this object.

### Sample Problem B

• A moving object has a KE equal to 300 J. A force is applied on the object in the same direction an increases it KE to 400 J. How much work was done on the object?

### Problem Set 2.1.1

• Pp. 93-94, #s 1-3, 6, and 9