Physical Science Chapter 11 Motion Physical Science Chapter 11

Physical Science chapter 11 Motion Can be described as a change in position. Physical Science chapter 11

Distance vs. displacement Distance is how far you traveled What your odometer reads Displacement is the distance between your starting point and your ending point, regardless of your path As the crow flies Physical Science chapter 11

Physical Science chapter 11 Speed How fast something moves The rate of change in position The rate of motion Rate means change over time Physical Science chapter 11

Physical Science chapter 11 Velocity vs. speed Velocity describes both speed and direction. Both “how fast” and “which way” something is moving Physical Science chapter 11

Physical Science chapter 11 Constant speed Speed that does not vary Cruise control Physical Science chapter 11

Physical Science chapter 11 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. Physical Science chapter 11

Physical Science chapter 11 Calculating speed If you know distance and time, you can calculate average speed. Physical Science chapter 11

Physical Science chapter 11 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 = ? Physical Science chapter 11

Physical Science chapter 11 Example continued Physical Science chapter 11

Physical Science chapter 11 You try Find the speed in meters per second of a baseball thrown 38 m from third base to first base in 1.7 s. Physical Science chapter 11

Physical Science chapter 11 Example Find the velocity in meters per second of a swimmer who swims 110 m toward the shore in 72 s. Physical Science chapter 11

Physical Science chapter 11 You try Calculate the displacement in meters that a cyclist would travel in 5.00 h at an average velocity of 12.0 km/h to the southwest. Remember to include direction. Physical Science chapter 11

Physical Science chapter 11 Instantaneous speed The rate of motion at a given instant Speedometer Physical Science chapter 11

Physical Science chapter 11 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. See pages 370–371 Discuss the practice problems Physical Science chapter 11

Physical Science chapter 11 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. Physical Science chapter 11

Physical Science chapter 11 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. Physical Science chapter 11

Calculating acceleration The triangle is the Greek letter delta, and stands for “change in” Physical Science chapter 11

Physical Science chapter 11 Units on acceleration Written as m/s2 Physical Science chapter 11

Physical Science chapter 11 Examples Natalie accelerates her skateboard along a straight path from 0.0 m/s to 4.0 m/s in 2.5 s. Find her average acceleration. Find the average acceleration of a northbound subway train that slows down from 12. m/s to 9.6 m/s in 0.8 s. Physical Science chapter 11

Acceleration on graphs On a speed vs. time graph (speed on the y-axis and time on the x-axis) Acceleration is the slope On a distance vs. time graph (distance on the y-axis and time on the x-axis) A curved line indicates acceleration A straight line indicates a constant velocity (no acceleration) Physical Science chapter 11

Physical Science chapter 11 Discuss Identify the straight-line accelerations below as either speeding up or slowing down 5.7 m/s2 -29.8 m/s2 -2.43 m/s2 9.8 m/s2 A turtle swimming in a straight line twoard shore ahs a speed of 0.50 m/s. After 4.0 s, its speed is 0.80 m/s. What is the turtle’s average acceleration? Physical Science chapter 11

Physical Science chapter 11 Force A push or a pull one object exerts on another Physical Science chapter 11

Physical Science chapter 11 Fundamental forces Gravity Electromagnetic force Like charges repel; opposite charges attract Strong force Holds nucleus together Weak force Involved with radioactivity Physical Science chapter 11

Contact forces vs. field forces Objects must be touching Field forces Don’t need to be touching Gravity, magnets, electric charges Physical Science chapter 11

Physical Science chapter 11 Balanced forces Forces that are equal in size and opposite in direction are called balanced forces. Tug-of-war tie Physical Science chapter 11

Physical Science chapter 11 Net Force When forces are unbalanced, there is a net force. A net force always causes a change in velocity. Could be a change is speed, a change in direction, or both. Physical Science chapter 11

Physical Science chapter 11 Friction The force that opposes motion between two surfaces that are touching each other. Enables us to walk, hold things, etc. Physical Science chapter 11

Physical Science chapter 11 Friction The amount of friction depends on two things The kinds of surfaces The force pressing the surfaces together More force  more friction Physical Science chapter 11

Physical Science chapter 11 Static Friction Between surfaces that aren’t moving Largest frictional force between any two objects Physical Science chapter 11

Physical Science chapter 11 Kinetic Friction Friction between moving surfaces Sliding friction Rolling friction Usually less than sliding friction Physical Science chapter 11

Physical Science chapter 11 Discuss What is a force? What are balanced forces? What is friction? Does a net force of zero mean that there is no force at all? Physical Science chapter 11