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Chapter 5: Force and Motion – I

Chapter 5: Force and Motion – I. Reading assignment: Chapter 5.5-5.8 Homework : (due Wednesday, Sept. 14, 2005) Chapter 5: 34, 38, 39, 48, 58, 66. In this chapter we will learn about the relationship between the force exerted on an object and the acceleration of the object. Forces

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Chapter 5: Force and Motion – I

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  1. Chapter 5: Force and Motion – I Reading assignment: Chapter 5.5-5.8 Homework : (due Wednesday, Sept. 14, 2005) Chapter 5: 34, 38, 39, 48, 58, 66 • In this chapter we will learn about the relationship between the force exerted on an object and the acceleration of the object. • Forces • Newton’s three laws.

  2. Contact forces - Involve physical contact between _________________.

  3. Field forces: • No _______________________ between objects • Forces act through __________ space gravity magnetic electric

  4. Measuring forces • Forces are often measured by determining the ___________________ of a calibrated spring. • ______________ are vectors!! Remember vector addition. • To calculate ________ force on an object you must use vector addition.

  5. Newton’s first law: • In the absence of external forces (no net force): • an object at rest __________ at rest • an object in motion continues in motion with constant _____________ (constant ____________, straight line) • (assume no _____________). Or: When no force acts on an object, the acceleration of the object is ____________________. Inertia: Object resists any attempt to change its _____________

  6. Inertial frame of reference: • A frame (system) that is not ____________________. • Newton’s laws hold true ____________ in non-accelerating (inertial) frames of reference! • Are the following inertial frames of reference: • A cruising car? • A braking car? • The earth? • Accelerating car?

  7. Mass • Mass of an object specifies how much inertia the object has. • Unit of mass is ___________. • The greater the mass of an object, the _____________ it accelerates under the action of an applied force. • Don’t confuse mass and ______________ (more later).

  8. Newton’s second law (Very important) • The acceleration of an object is: • directly ____________ to the net force acting on it • and ___________ proportional to its mass.

  9. Unit of force: • The unit of force is the Newton (1N) • One Newton: The force required to _______________ a 1 kg mass by 1m/s2. • 1N = 1______/s2

  10. Black board example 5.1 F2 = 8.0 N q2 = 60° F1 = 5.0 N q1 = - 20° Two forces act on a hockey puck (mass 0.3 kg) as shown in the figure. • Determine the magnitude and direction of the net force acting on the puck • Determine the magnitude and the direction of the pucks acceleration. • What third force (direction and magnitude) would need to be applied to the puck so that its acceleration is zero?

  11. The force of gravity and weight • Objects are attracted to the Earth. • This attractive force is the force of gravity Fg. • The ________ of this force is called the weight of the object. • Thus, the weight of an object is _______ (Force required to keep mass m from falling to the ground). The weight of an object can very with _____________ (less weight on the moon than on earth, since g is smaller). The mass of an object does not vary. Don’t confuse mass and weight

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