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Apr-15General Science Chapter 21 Chapter 2 Moving Objects  Motion  Speed  Instantaneous Speed  Constant Speed  Average Speed  Velocity  Acceleration.

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Presentation on theme: "Apr-15General Science Chapter 21 Chapter 2 Moving Objects  Motion  Speed  Instantaneous Speed  Constant Speed  Average Speed  Velocity  Acceleration."— Presentation transcript:

1 Apr-15General Science Chapter 21 Chapter 2 Moving Objects  Motion  Speed  Instantaneous Speed  Constant Speed  Average Speed  Velocity  Acceleration  Force  Net Force  Balanced Forces  Inertia  Friction  Gravity  Weight  Mass

2 Apr-15General Science Chapter 22 Section 1 Motion  Motion  Speed  Instantaneous Speed  Constant Speed  Average Speed  Velocity  Acceleration

3 Apr-15General Science Chapter 23 Motion  You don’t have to see something move to know that motion has taken place.  You only have to know that its position has changed. Best described as a change in position.  You need a reference point to know if position has changed.  Depends on the observer’s frame of reference.

4 Apr-15General Science Chapter 24 Speed  How fast something moves  The rate of change in position  The distance traveled in a given amount of time  The rate of motion  Rate means change over time

5 Apr-15General Science Chapter 25 Instantaneous speed  The rate of motion at a given instant Speedometer

6 Apr-15General Science Chapter 26 Constant speed  Speed that does not vary Cruise control

7 Apr-15General Science Chapter 27 Average speed  Total distance traveled divided by total time of travel  Used when the object in motions makes changes in speed, including starts and stops.

8 Apr-15General Science Chapter 28 Calculating speed  If you know distance and time, you can calculate speed.

9 Apr-15General Science Chapter 29 Example  You skate a distance of 100 m in 67 s. What is your average speed?  Known: d = 100 m t = 67 s  Unknown v = ?

10 Apr-15General Science Chapter 210 Example continued

11 Apr-15General Science Chapter 211 Graphing speed  When distance is graphed on the y-axis and time is graphed on the x-axis, we call this a distance-time graph.  The slope of a distance-time graph is the speed.  What kind of graph would you use to graph distance vs time?

12 Apr-15General Science Chapter 212 Section 1: Discussion Questions  What is motion?  What two quantities do you need to know to calculate average speed?  What does a flat line on a segment of a distance-time graph tell you about the average speed for that time period?

13 Apr-15General Science Chapter 213 Velocity vs. speed  Velocity describes both speed and direction.  Speed describes only rate of change in position.

14 Apr-15General Science Chapter 214 REVIEW #1  What is the difference between instantaneous and average speed?  What is the difference between speed and velocity?  What is the equation used to solve for average speed?  What SI units are used for speed?  What is motion?

15 Apr-15General Science Chapter 215 Acceleration  The rate of change of velocity.  Acceleration occurs if either the speed or direction changes, or if both change.  “Slowing down” is a change in speed, so when something slows down, it is accelerating.  When speed decreases, acceleration is opposite in direction to velocity.

16 Apr-15General Science Chapter 216 Acceleration  The size of acceleration depends on both the change in velocity and the time interval over which the change takes place  If the change in velocity is large, the acceleration will be large.  If the time interval is short, then acceleration will be large.

17 Apr-15General Science Chapter 217 Calculating acceleration  The triangle is the Greek letter delta, and stands for “change in”

18 Apr-15General Science Chapter 218 Units on acceleration  Meters per second per second or  Meters per second squared  Written as m/s 2

19 Apr-15General Science Chapter 219 Example  A car increases its velocity from 10 m/s to 32 m/s in 3 seconds. What is the acceleration of the car?  Known: v i = 10 m/s v f = 32 m/s t = 3 s  Unknown: a=?

20 Apr-15General Science Chapter 220 Example continued

21 Apr-15General Science Chapter 221 Discussion Questions, Part 2  What is acceleration?  What are three ways an object can accelerate?  What equation is used to determine acceleration?  What is the SI unit of acceleration?  Is the SI unit of acceleration a derived unit?

22 Apr-15General Science Chapter 222 Section 2 Forces  Force  Balanced Forces  Net Force  Inertia  Friction

23 Apr-15General Science Chapter 223 Force  A push or a pull one object exerts on another

24 Apr-15General Science Chapter 224 Balanced forces  Forces that are equal in size and opposite in direction are called balanced forces.  Tug-of-war

25 Apr-15General Science Chapter 225 Net Force  When forces are unbalanced, there is a net force.  A net force always causes a change in velocity.  Could be a change in speed, a change in direction, or both.

26 Apr-15General Science Chapter 226 Inertia  The tendency of an object to resist any change in its motion.  If it is moving, it tends to keep moving at the same velocity unless a force acts on it.  If it is not moving, it tends to remain at rest unless a force acts on it.

27 Apr-15General Science Chapter 227 Mass and inertia  The more mass an object has, the greater its inertia is.  Objects with greater inertia take more force to change their velocity.

28 Apr-15General Science Chapter 228 Newton’s first law  An object moving at a constant velocity keeps moving at that velocity unless a net force acts on it.  An object at rest stays at rest unless a net force acts on it.  An object at rest/in motion will stay at rest/in motion unless a net force acts on it.  Also called the law of inertia.

29 Apr-15General Science Chapter 229 Seatbelts  When a car crashes, a force stops the car and any passengers in the car.  A passenger who isn’t wearing her seatbelt isn’t acted on by the force of the seatbelt, so she keeps moving at the same velocity.

30 Apr-15General Science Chapter 230 Friction  The force that opposes motion between two surfaces that are touching each other.  Enables us to walk, hold things, etc.

31 Apr-15General Science Chapter 231 Friction  The amount of friction depends on two things The kinds of surfaces The force pressing the surfaces together

32 Apr-15General Science Chapter 232 Discuss  What is a force?  What are balanced forces?  What is inertia?  What is friction?

33 Apr-15General Science Chapter 233 Section 3 Gravity  Gravity  Weight  Mass  Scales

34 Apr-15General Science Chapter 234 Gravity  Every object in the universe exerts a force on every other object That force is gravity  Often, the force is too small to notice Example – the force of gravity between two people

35 Apr-15General Science Chapter 235 Gravitational force  The amount of gravitational force between two objects depends on two things Their masses and the distance between them.  The mass of a person is small, so the gravitational force between two people is weak.  The mass of the Earth is large, so the gravitational force between the Earth and a person is strong.

36 Apr-15General Science Chapter 236 Gravitational force  Gets weaker as the distance increases

37 Apr-15General Science Chapter 237 Weight  The measure of the force of gravity on an object.  We usually use the term weight when we talk about the gravitational force between the Earth and an object near its surface.

38 Apr-15General Science Chapter 238 Weight  Related to mass  Objects with greater mass have greater weight.  Weight is determined by the gravitational pull on the object.

39 Apr-15General Science Chapter 239 Weight and mass  Weight is measured in Newtons (N).  1 kg of mass at the Earth’s surface has a weight of 9.8 N

40 Apr-15General Science Chapter 240 Weight on Earth vs. Weight on Moon  Since the Earth has more mass than the moon, it exerts a greater gravitational force than the moon.  So, things weigh less on the moon than they do on Earth.  Do they have less mass on the moon?

41 Apr-15General Science Chapter 241 Scales  Use the principal of balanced forces to measure how much something weighs.  Scales use springs to balance the force of an object’s weight.

42 Apr-15General Science Chapter 242 Discuss  What is the force of gravity?  What is weight?  Weight is measured in what SI units?  What instrument is used to measure weight?

43 Apr-15General Science Chapter 243 Chapter Review  Do you know the difference between: Speed and velocity Average speed and instantaneous speed Motion and speed Balanced forces and net forces Mass and Weight A balance and a scale


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