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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.

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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


  • 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

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