Matter in Motion


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Holt Science & Technology - Physical Science Series

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Matter in Motion

  1. 1.  Take out your vocab sheet from yesterday and have it laying on your desk so I can look at it. Describe your position in the classroom compared to something else in the classroom(a reference point) and a set of reference directions. WARMUP
  2. 2. Book M1 Chapter 1MATTER IN MOTION
  3. 3. By the end of this section, you should be able to:  Describe the motion of an object by the position of the object in relation to a reference point.  Identify the two factors that determine speed.  Explain the difference between speed and velocity.  Analyze the relationship between velocity and acceleration.  Demonstrate that changes in motion can be measured and represented on a graph. SECTION 1: MEASURING MOTION
  4. 4.  Motion is an object’s change in position relative to another object, or reference point.  The object that appears to stay in place is called a reference point. OBSERVING MOTION USING A REFERENCE POINT
  5. 5.  The direction of an object’s motion can be described with a reference direction, such as north, south, east, west, up, or down.  The Earth’s surface is a common reference point for determining motion. OBSERVING MOTION USING A REFERENCE POINT
  6. 6.  Speed is the distance traveled by an object divided by the time taken to travel that distance.  The SI unit for speed is meters per second (m/s). Kilometers per hour (km/h), feet per second (ft/s), and miles per hour (mi/h) are other units commonly used to express speed. SPEED DEPENDS ON DISTANCE AND TIME
  8. 8. 2 cars both travel at 65 mi/h for 3 hours.  How far did they travel?  Why didn’t they end up at the same place? WARMUP
  9. 9.  Speed can be shown on a graph of distance versus time. SPEED DEPENDS ON DISTANCE AND TIME
  10. 10.  The speed of an object in a particular direction is called velocity.  Speed and velocity have two different meanings. Velocity must include a reference direction. VELOCITY: DIRECTION MATTERS
  11. 11.  You can think of velocity as the rate of change of an object’s position. An object’s velocity is constant only if its speed and direction don’t change.  You can combine different velocities to find the resultant velocity. VELOCITY: DIRECTION MATTERS
  12. 12.  The rate at which velocity changes over time is called acceleration. An object accelerates if its speed, or direction, or both change.  An increase in velocity is commonly called positive acceleration. A decrease in velocity is commonly called negative acceleration, or deceleration. ACCELERATION
  14. 14. Complete the problem inside the Math Practice box on p.8 CALCULATING AVERAGE ACCELERATION
  15. 15.  Acceleration can be shown on a graph of velocity versus time. ACCELERATION
  16. 16.  An object traveling in a circular motion is always changing its direction. Therefore, its velocity is always changing, so it is accelerating.  The acceleration that occurs in circular motion is known as centripetal acceleration. CIRCULAR MOTION: CONTINUOUS ACCELERATION
  17. 17.  Section Review p.9 #3-10 HOMEWORK
  18. 18. By the end of this section, you should be able to:  Describe forces, and explain how forces act on objects.  Determine the net force when more than one force is acting on an object.  Compare balanced and unbalanced forces.  Describe ways that unbalanced forces cause changes in motion. SECTION 2: WHAT IS A FORCE?
  19. 19.  In science, a force is simply a push or a pull exerted on an object in order to change the motion of the object.  All forces have both size and direction.  A force can change the acceleration of an object. This acceleration can be a change in the speed or direction of the object. FORCES ACTING ON OBJECTS
  20. 20.  Scientists express force using a unit called the newton (N).  It is not always easy to tell what is exerting a force or what is receiving a force. For example, you cannot see what exerts the force that pulls magnets to refrigerators.  You cannot see that the air around you is held near Earth’s surface by a force called gravity. FORCES ACTING ON OBJECTS
  21. 21.  Usually, more than one force is acting on an object. The net force is the combination all of the forces acting on an object.  Determining net force depends on the directions of the forces. DETERMINING NET FORCE
  22. 22.  Two forces are added to determine the net force if the forces act in the same direction. The net force will be in the same direction as the individual forces.  If forces are acting in opposite directions, the net force can be found by subtracting the smaller force from the larger one. DETERMINING NET FORCE
  23. 23.  When the forces on an object produce a net force of 0 N, the forces are balanced.  Balanced forces will not cause a change in the motion of a moving object.  Balanced forces do not cause a nonmoving object to start moving. BALANCED AND UNBALANCED FORCES
  24. 24.  When the net force on an object is not 0 N, the forces on the object are unbalanced.  Unbalanced forces produce a change in motion, such as a change in speed or a change in direction.  Unbalanced forces are necessary to cause a non- moving object to start moving, or to change the motion of moving objects. BALANCED AND UNBALANCED FORCES
  25. 25.  P.13 #1-9 HOMEWORK
  26. 26. By the end of this section, you should be able to:  Explain why friction occurs.  List the two types of friction, and give examples of each type.  Explain how friction can be both harmful and helpful. SECTION 3: FRICTION – A FORCE THAT OPPOSES MOTION
  27. 27.  Friction is a force that opposes motion between two surfaces that are in contact.  Friction occurs because the surface of any object is rough. Even surfaces that feel smooth are covered with microscopic hills and valleys. SOURCES OF FRICTION
  28. 28.  When two surfaces are in contact, the microscopic hills and valleys of one surface stick to the tiny hills and valleys of the other surface. This contact causes friction.
  29. 29.  The amount of friction depends on the force pushing the surfaces together.  If this force increases, the hills and valleys of the surfaces can come into closer contact. The close contact increases the friction between the surfaces.  Objects that weigh less exert less downward force than objects that weigh more. SOURCES OF FRICTION
  30. 30.  Rough surfaces have more microscopic hills and valleys than smooth surfaces do. So, the rougher the surface is, the greater the friction is. SOURCES OF FRICTION
  31. 31.  The word kinetic means “moving.” So, kinetic friction is friction between moving surfaces.  The amount of kinetic friction between two surfaces depends in part on how the surfaces move. Surfaces can slide past each other, or a surface can roll over another surface. TYPES OF FRICTION
  32. 32.  Usually, the force of sliding kinetic friction is greater than the force of rolling kinetic friction. It is usually easier to move objects on wheels than to slide the objects along the floor. TYPES OF FRICTION
  33. 33.  When a force is applied to an object but does not cause the object to move, static friction occurs.  The word static means “not moving.” The object does not move because the force of static friction balances the force applied.  Static friction disappears as soon as an object starts moving, and then kinetic friction immediately occurs. TYPES OF FRICTION
  34. 34.  Without friction, a car’s tires could not push against the ground to move the car forward, and the brakes could not stop the car. Without friction, a car is useless.  However, friction can also cause problems in a car. Friction between moving engine parts increases their temperature and causes the parts to wear down. FRICTION: HARMFUL AND HELPFUL
  35. 35.  Friction can be both harmful and helpful, so it may be necessary to decrease or increase friction.  One way to reduce friction is to use lubricants. Lubricants are substances that are applied to surfaces to reduce the friction between the surfaces.  Some examples of common lubricants are motor oil, wax, and grease. Lubricants are usually liquids, but they can be solids or gases. FRICTION: HARMFUL AND HELPFUL
  36. 36.  Friction can be reduced by switching from sliding kinetic friction to rolling kinetic friction. Ball bearings can be placed between wheels and axles to make it easier for wheels to turn by reducing friction.  Another way to reduce friction is to make surfaces that rub against each other smoother. FRICTION: HARMFUL AND HELPFUL
  37. 37.  Making surfaces rougher is one way to increase friction. For example, sand scattered on icy roads keeps cars from skidding.  Another way to increase friction is to increase the force pushing the surfaces together. For example, if you are sanding a piece of wood, you can sand the wood faster by pressing harder on the sandpaper. FRICTION: HARMFUL AND HELPFUL
  38. 38. HOMEWORK
  39. 39. By the end of this section, you should be able to:  Describe gravity and its effect on matter.  Explain the law of universal gravitation.  Describe the difference between mass and weight. SECTION 4: GRAVITY – A FORCE OF ATTRACTION
  40. 40.  Gravity is a force of attraction between objects that is due to their masses.  Gravity can change the motion of an object by changing its speed, direction, or both.  All matter has mass, and gravity is a result of mass. Therefore, all matter is affected by gravity and all objects experience an attraction toward all other objects. THE EFFECTS OF GRAVITY ON MATTER
  41. 41.  The mass of most objects is too small to cause a force large enough to move objects toward each other.  Compared with all objects around you, Earth has a huge mass. Therefore, Earth’s gravitational force is very large.  You must apply forces to overcome the Earth’s gravitational force any time you lift objects or even parts of your body. THE EFFECTS OF GRAVITY ON MATTER
  42. 42.  Why do objects fall toward the Earth? What keeps the planets moving in the sky?  In 1665, British scientist Sir Isaac Newton made the connection between these two questions when, as legend has it, he saw an apple falling from a tree. NEWTON & THE STUDY OF GRAVITY
  43. 43.  Newton knew that unbalanced forces are needed to change the motion of objects. He concluded that an unbalanced force on the apple made the apple fall.  He also reasoned that an unbalanced force on the moon kept the moon moving around the Earth.  He proposed that these two forces are actually the same force – gravity. NEWTON & THE STUDY OF GRAVITY
  44. 44.  Newton summarized his ideas about gravity in a law known as the law of universal gravitation.  This law describes the relationships between gravitational force, mass, and distance.  The law is called universal because it applies to all objects in the universe. NEWTON & THE STUDY OF GRAVITY
  45. 45.  Gravitational force is small between objects that have small masses. Gravitational force is large when the mass of one or both objects is large.  Gravitational force is strong when distance between two objects is small. If the distance between two objects increases, the gravitational force pulling them together decreases rapidly. LAW OF UNIVERSAL GRAVITATION
  46. 46.  Weight is related to mass, but they are not the same.  Weight is a measure of the gravitational force on an object. Weight changes whenever gravitational force changes.  Mass is the amount of matter in an object. An object’s mass does not change if gravitational force changes. WEIGHT AS A MEASURE OF GRAVITATIONAL FORCE
  47. 47.  The SI unit of force is a newton (N). Gravity is a force, and weight is a measure of gravity. So, weight is also measured in newtons.  The SI unit of mass is the kilogram (kg). Mass is often measured in grams (g) and milligrams (mg) as well.  On Earth, a 100 g object weighs about 1 N. WEIGHT AS A MEASURE OF GRAVITATIONAL FORCE
  48. 48. HOMEWORK