1 / 24

Mechanical Equilibrium

Mechanical Equilibrium. Chapter 2. Equilibrium. What is equilibrium? Balanced budget Glass thermometer reaching same temp as surroundings Equilibrium is achieved when an object is stable, without changes in motion. Jump rope example Did the rope remain straight?

allene
Télécharger la présentation

Mechanical Equilibrium

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MechanicalEquilibrium Chapter 2

  2. Equilibrium • What is equilibrium? • Balanced budget • Glass thermometer reaching same temp as surroundings • Equilibrium is achieved when an object is stable, without changes in motion. • Jump rope example • Did the rope remain straight? • Is there any way to make the rope stay straight when someone is pushing on the center? • What do you think are the conditions necessary for equilibrium?

  3. Net Force • There is usually more than one force acting on an object • Combination of all forces acting on an object is the netforce—this is what changes its motion

  4. Force • A force is a push or a pull • Always required to change the state of motion of an object • A hockey puck at rest will stay at rest and a puck in motion will stay in motion • A force is needed to change an object’s state of motion

  5. Tension and Weight • Spring scales • Stretching force is called tension • In science, we measure force in terms of Newtons (N) • 2 Forces acting on the fish • Equal and opposite • What is the net force?

  6. Vectors • Forces are represented by arrows • http://www.youtube.com/watch?v=A05n32Bl0aY • When the length of an arrow is scaled to represent the amount (magnitude) the arrow is called a vector • Vector is an arrow that represents the magnitude and direction of a quantity.

  7. Quantities • Vector Quantity • A quantity that needs both magnitude and direction for a complete description • Scalar Quantity • A quantity that can be described by magnitude only and has no direction.

  8. On your board (OYB): How can you change an object’s state of motion?

  9. Mechanical Equilibrium • Mechanical equilibrium is a state wherein no physical changes occur; it is a state of steadiness. • The equilibrium rule states that whenever the net force on an object is zero, the object is said to be in mechanical equilibrium. Expressed mathematically: ∑ F=0

  10. Mechanical Equilibrium • Remember that vector quantities take into account direction • So upward forces must be positive and downward counted as negative

  11. OYB:How can you express the equilibrium rule mathematically?

  12. Support Force • What about my book on the podium? • Where does the upward force come from? • Support Force is the upward force that balances the weight of an object on a surface. (Also referred to as normal force) • Book and spring • Spring would push up with as much force as you push down—book compresses atoms which act like microscopic springs

  13. Support Force • Step on a scale: what two forces act on the scale? • Forces compress a mechanism, like a spring, that is calibrated to show the support force, your weight

  14. OYB:While standing on the scale what can be said about the magnitude of the support force and your weight?What is the net force on a bathroom scale when a 110 pound person stands on it?

  15. OYB:Suppose you stand on two bathroom scales with your weight evenly distributed between the two scales. That is the reading on each of the scales? What happens when you stand with more of your weight on one foot than the other?

  16. Equilibrium for Moving Objects • Equilibrium is a state of no change, but that includes more than just not moving. • Would an object under the influence of only one force be in equilibrium? • A desk being pushed along the floor, if it stays at a constant speed

  17. OYB • An airplane flies horizontally at constant speed in a straight-line direction. Its state of motion is unchanging. In other words, it is in equilibrium. Two horizontal forces act on the plane. One is the thrust of the propeller that pulls it forward. The other is the force of air resistance (air friction) that acts in the opposite direction. Which force is greater?

  18. Equilibrium • Objects at rest are said to be in static equilibrium. • Objects at constant speed in a straight line path are said to be in dynamic equilibrium. • In the car of a train…

  19. OYBHow are static and dynamic equilibrium different?

  20. Vectors • If a gymnast is suspended by a single vertical strand of rope, tension would equal the gymnast's weight, lets say 300N • If she hangs by two vertical strands, what could we expect the tension on the ropes to become? • What two forces are acting on the gymnast?

  21. Vectors • Combining vectors when they are parallel is simple, if in the same direction, they add • The sum of two or more vectors is called their resultant • To find the resultant of two non-parallel vectors, construct a parallelogram wherein two vectors are adjacent sides. The diagonal of the parallelogram shows the resultant. • The diagonal is the resultant R

  22. Parallelogram Rule • http://www.youtube.com/watch?v=zwyUjFzLsuQ • So what is the answer to his question? • Can you break a guitar string by pulling on its ends? How can you break one? • Vertical vs. horizontal clothesline

  23. OYBConsider what would happen if you suspended a 10-N object midway along a very tight, horizontally stretched guitar string. Is it possible for the string to remain horizontal without a slight sag at the point of suspension?

  24. Practice • Pages 25-26 • Questions 21-31, 37-38, 40-41, 42-48

More Related