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PHSC 1011 Chapter 1 Patterns of Motion and Equilibrium.

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Presentation on theme: "PHSC 1011 Chapter 1 Patterns of Motion and Equilibrium."— Presentation transcript:

1 PHSC 1011 Chapter 1 Patterns of Motion and Equilibrium

2 1.1 Aristotle on Motion Two Kinds of Motion – Natural and Violent Natural Motion depends on the Nature of the Object. An object has a “proper place” and, if not there, will strive to get there. Natural Motion is straight up or straight down. All motion on the Earth is linear. All motion in the heavens (outer space) is curved.

3 1.1 Aristotle on Motion Violent Motion is imposed motion caused by pushing or pulling. Motion continues only so long as there is an applied force to an object. Removing the force stops the object. The speed at which an object falls is directly related to the mass of an object. It would take a man named Galileo to start the wheels of change in this field of knowledge called physics.

4 1.2 Galileo’s Concept of Inertia According to Galileo, the motion of a falling object is independent of mass - two objects of unequal masses will fall to the ground when dropped from a set height in equal times According to Galileo, the motion of a falling object is independent of mass - two objects of unequal masses will fall to the ground when dropped from a set height in equal times The reason why objects did not always fall in the same time was because of a retarding force called friction. The reason why objects did not always fall in the same time was because of a retarding force called friction. Once an object is set in motion, it will remain in motion without the application of a force except as necessary to overcome friction. Once an object is set in motion, it will remain in motion without the application of a force except as necessary to overcome friction.

5 1.2 Galileo’s Concept of Inertia Galileo did an experiment by rolling balls in a tray with sloped sides. He observed that the balls increased in speed going downhill, maintained constant speed on the level, and decreased in speed going uphill. He concluded that if friction were not present, the ball moving on the level would continue at the same speed indefinitely. He also noted that objects at rest tend to remain at rest. This resistance an object has to a change in its state of motion is called INERTIA.

6 1.2 Galileo’s Concept of Inertia

7 1.3 Mass – a Measure of Inertia The amount of inertia an object possesses depends upon the amount of matter in the object – the more matter, the greater the inertia. The amount of inertia an object possesses depends upon the amount of matter in the object – the more matter, the greater the inertia. The term, MASS, is used to describe the amount of matter in an object. The greater and object’s mass, the greater the magnitude of its inertia. The term, MASS, is used to describe the amount of matter in an object. The greater and object’s mass, the greater the magnitude of its inertia. Therefore, mass can be used as a measure of an object’s inertia. Therefore, mass can be used as a measure of an object’s inertia.

8 1.3 Mass – a Measure of Inertia Mass Versus Weight Mass is a measure of the amount of material in an object and also it’s inertia. Mass is a measure of the amount of material in an object and also it’s inertia. Weight is the force upon an object due to gravity. Weight is the force upon an object due to gravity. Mass and Weight are proportional to each other Mass and Weight are proportional to each other

9 1.3 Mass – a Measure of Inertia Mass Versus Weight Mass is measured in kilograms (kg). Mass is measured in kilograms (kg). One kilogram weighs 9.8 newtons (N). One kilogram weighs 9.8 newtons (N). One kilogram of mass weighs 2.2 lb. One kilogram of mass weighs 2.2 lb. One pound is equivalent to 4.45 N. One pound is equivalent to 4.45 N.

10 1.3 Mass – a Measure of Inertia Mass Versus Weight

11 1.4 Net Force A force is a push or a pull. A force is a push or a pull. An object does not speed up, slow down, or change direction unless a force acts upon it. An object does not speed up, slow down, or change direction unless a force acts upon it. An object moving through the atmosphere and/or in contact with the Earth have a variety of forces acting upon it, for example: aerodynamic drag, gravity, and mechanical friction. An object moving through the atmosphere and/or in contact with the Earth have a variety of forces acting upon it, for example: aerodynamic drag, gravity, and mechanical friction. The NET FORCE on the object is a combination of all forces acting upon it. The NET FORCE on the object is a combination of all forces acting upon it.

12 1.4 Net Force

13 1.5 The Equilibrium Rule When the combination of all forces acting upon an object add up to a zero net force (that is – they cancel each other out) the object is said to be in Mechanical Equilibrium. When the combination of all forces acting upon an object add up to a zero net force (that is – they cancel each other out) the object is said to be in Mechanical Equilibrium.  F = 0

14 1.5 The Equilibrium Rule

15 1.6 Support Force When an object sits on a surface, gravity pulls the object downward. When an object sits on a surface, gravity pulls the object downward. Since the object remain motionless, the net force must be zero. Since the object remain motionless, the net force must be zero. Therefore the surface is exerting a Support Force upward upon the book. Therefore the surface is exerting a Support Force upward upon the book.

16 1.6 Support Force

17 1.7 Equilbrium of Moving Things Equilibrium is a state of no change. Equilibrium is a state of no change. An object at rest is at equilibrium. An object at rest is at equilibrium. An object moving at a constant speed in a straight line is in equilibrium. An object moving at a constant speed in a straight line is in equilibrium. Question: Can an object being subjected to a single force be in equilibrium? Question: Can an object being subjected to a single force be in equilibrium?

18 1.8 The Force of Friction Friction always acts in a direction to oppose motion. Friction always acts in a direction to oppose motion. The amount of friction between two surfaces depends on the kinds of material and how tightly they are pressed together. The amount of friction between two surfaces depends on the kinds of material and how tightly they are pressed together. Friction is caused by tiny surface bumps and the “stickiness” of the atoms on the surfaces of the two materials. Friction is caused by tiny surface bumps and the “stickiness” of the atoms on the surfaces of the two materials.

19 1.8 The Force of Friction

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21 1.9 Speed and Velocity Speed is the distance traveled in a given time. Speed is the distance traveled in a given time. Speed = Distance Traveled Travel Time Instantaneous Speed is the speed at a given instant. Instantaneous Speed is the speed at a given instant. Average speed is the total distance covered divided by the total time for the trip. Average speed is the total distance covered divided by the total time for the trip.

22 1.9 Speed and Velocity Velocity is combination of Speed and Direction of Travel. Velocity is combination of Speed and Direction of Travel. Constant Velocity is constant speed and constant direction – motion in a straight line at constant speed. Constant Velocity is constant speed and constant direction – motion in a straight line at constant speed. All things in the universe are moving. All things in the universe are moving. When we discuss speed or velocity, we are talking about speed or velocity relative to something else (usually the surface of the Earth). When we discuss speed or velocity, we are talking about speed or velocity relative to something else (usually the surface of the Earth).

23 1.10 Acceleration When the rate of motion of an object changes, we say that the object is undergoing Acceleration. When the rate of motion of an object changes, we say that the object is undergoing Acceleration. Acceleration is defined as the rate of change of velocity. Acceleration is defined as the rate of change of velocity. Acceleration = Change in Velocity Time Interval

24 1.10 Acceleration

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