Section 1 Measuring Motion Chapter 10 Bellringer Everybody knows what motion is, but how do you measure it? • One way is to measure distance, how far something goes during a motion. • Another is to measure time, how long a motion takes to occur. • A third way is to measure speed, how fast something is moving. Each of the devices shown below can be used to measure some aspect of motion.

Section 1 Measuring Motion Chapter 10 Bellringer, continued • For each of the devices above, indicate whether it measures distance, time, or speed. • For each of the devices above, indicate which of the following units are possible for a measurement: meters (m), seconds (s), or meters per second (m/s).

Section 1 Measuring Motion Chapter 10 Observing Motion • Motion is an object’s change in position relative to a reference point. • Displacement is the change in the position of an object. • Distance measures the path taken. • Displacement is the change of an object’s position. Displacement must always indicate direction.

Section 1 Measuring Motion Chapter 10 Distance vs. Displacement

Section 1 Measuring Motion Chapter 10 Speed and Velocity • Speed is the distance traveled divided by the time interval during which the motion occurred. Speed describes how fast an object moves. • Speed measurements involve distance and time. • The SI units for speed are meters per second (m/s). • When an object covers equal distances in equal amounts of time, it is moving at a constantspeed.

Section 1 Measuring Motion Chapter 10 Speed and Velocity, continued • Speed can be studied with graphs and equations. • Speed can be determined from a distance-time graph. When an object’s motion is graphed by plotting distance on the y-axis and time on the x-axis, the slope of the graph is speed.

Section 1 Measuring Motion Chapter 10 Speed and Velocity, continued • Average speedis calculated as distance divided by time. Equation for Average Speed • Instantaneous speedis the speed at a given point in time.

Section 1 Measuring Motion Chapter 10 Math Skills VelocityMetal stakes are sometimes placed in glaciers to help measure a glacier’s movement. For several days in 1936, Alaska’s Black Rapids glacier surged as swiftly as 89 meters per day down the valley. Find the glacier’s velocity in m/s. Remember to include direction. • List the given and the unknown values. Given: time,t = 1 day displacement,d = 89 m down the valley Unknown: velocity, v = ? (m/s and direction)

Section 1 Measuring Motion Chapter 10 Math Skills, continued 2. Perform any necessary conversions. To find the velocity in meters per second, the value for time must be in seconds.

Section 1 Measuring Motion Chapter 10 Math Skills, continued 3. Write the equation for speed. 4. Insert the known values into the equation, and solve.

Section 1 Measuring Motion Chapter 10 Speed and Velocity, continued • Velocityis the speed of an object in a particular direction. • Velocity describes both the speed and the direction. • Combine velocities to determine theresultant velocity.

Section 2 Acceleration Chapter 10 Objectives • Describethe concept of acceleration as a change in velocity. • Explainwhy circular motion is continuous acceleration even when the speed does not change. • Calculateacceleration as the rate at which velocity changes. • Graphacceleration on a velocity-time graph.

Section 2 Acceleration Chapter 10 Bellringer Which of the following examples shows a change in velocity? Remember a change in velocity can be either a change in speed or a change in the direction of motion. Briefly explain your answer. a. a car coming to a stop at a stop sign b. a book sitting on a desk c. a yo-yo in motion d. a bicyclist making a left-hand turn at exactly 15 km/h

Section 2 Acceleration Chapter 10 Bellringer, continued In the picture shown above, the student pulls on the box with the rope. If the box is originally not moving, will its velocity increase or stay the same? In which direction (if any) will the velocity be after the student pulls on the box with the rope?

Section 2 Acceleration Chapter 10 Acceleration and Motion • Acceleration is the rate at which velocity changes over time. • An object accelerates if its speed, direction, or both change.

Section 2 Acceleration Chapter 10 Acceleration and Motion, continued • Acceleration can be a change in speed. • Acceleration can be a change in direction. • Uniform circular motionis constant acceleration.

Section 2 Acceleration Chapter 10 Calculating Acceleration • Acceleration is the rate at which velocity changes. Acceleration Equation (for straight-line motion) • In SI units, acceleration is measured in meters per second per second (m/s/s) or m/s2.

Section 2 Acceleration Chapter 10 Math Skills AccelerationA flowerpot falls off a second-story windowsill. The flowerpot starts from rest and hits the sidewalk 1.5 s later with a velocity of 14.7 m/s. Find the average acceleration of the flowerpot. 1. List the given and the unknown values. Given: time,t = 1.5 s initial velocity,vi = 0 m/s final velocity,vf = 14.7 m/s down Unknown: acceleration, a = ? (m/s2 and direction)

Section 2 Acceleration Chapter 10 Math Skills, continued 3. Insert the known values into the equation, and solve. 2. Write the equation for acceleration.

Section 2 Acceleration Chapter 10 Calculating Acceleration, continued Acceleration can be determined from a velocity-time graph.

Section 3 Motion and Force Chapter 10 Objectives • Explainthe effects of unbalanced forces on the motion of objects. • Compareand contraststatic and kinetic friction. • Describehow friction may be either harmful or helpful. • Identifyways in which friction can be reduced or increased.

Section 3 Motion and Force Chapter 10 Bellringer The concept of force explains many occurrences in our everyday lives. From your own experience, state what will happen in the following situations: • A marble is placed at the top of a smooth ramp. What happens to the marble? What force causes this? • A marble is rolling around in the back of a small toy wagon as the wagon is pulled along the sidewalk. When the wagon is stopped suddenly by a rock under one of the wheels, the marble rolls towards the front of the wagon. Why does the marble keep going when the wagon stops? (Hint: Consider what it takes to change the velocity of the wagon and the marble.) • If you dropped a flat uncrumpled sheet of notebook paper and a similar piece of notebook paper that was crushed into a ball from the same height, which would reach the floor first? Why are the forces on these two pieces of paper different?

Section 3 Motion and Force Chapter 10 Balanced and Unbalanced Forces • Forceis an action exerted on a body in order to change the body’s state of rest or motion. Force has magnitude and direction. • Thenet forceis the combination of all forces acting on an object. • Objects subjected to balancedforceseither do not move or move at constant velocity. • An unbalanced forcemust be present to cause any change in an object’s state of motion or rest.

Section 3 Motion and Force Chapter 10 The Force of Friction • Friction is a force that opposes motion between two surfaces that are in contact. • Friction opposes the applied force.

Section 3 Motion and Force Chapter 10 The Force of Friction, continued • Static frictionresists the initiation of sliding motion between two surfaces that are in contact and at rest. • Kinetic frictionopposes the movement of two surfaces that are in contact and are sliding over each other. • Static friction is greater than kinetic friction. • There are many different types of kinetic friction, such as sliding frictionandrolling friction. • Fluid friction, such as air resistance, also opposes motion.

Section 3 Motion and Force Chapter 10 Frictional Forces and Acceleration

Section 3 Motion and Force Chapter 10 Friction and Motion • Friction can be helpful or harmful. • Friction is necessary to roll a vehicle or hold an object. • However, friction can also cause excessive heating or wear of moving parts. • Harmful friction can be reduced. • Helpful friction can be increased.

Standardized Test Prep Chapter 10 Understanding Concepts 1. A bicyclist traveling at 10 m/s applies her brakes, reducing her velocity to 5 m/s. If it takes 2 seconds to slow the bike, what is the acceleration during that period? A. –5 m/s2 B. –2.5 m/s2 C. 0 m/s2 D. 2.5 m/s2

Standardized Test Prep Chapter 10 Understanding Concepts, continued 1. A bicyclist traveling at 10 m/s applies her brakes, reducing her velocity to 5 m/s. If it takes 2 seconds to slow the bike, what is the acceleration during that period? A. –5 m/s2 B. –2.5 m/s2 C. 0 m/s2 D. 2.5 m/s2

Chapter 10 Standardized Test Prep Understanding Concepts, continued 2. What happens to a moving object when the forces acting on it are exactly balanced? F. The object gradually slows and stops moving due to friction. G. The object moves at a constant speed, neither speeding up nor slowing down. H. The object accelerates because there is no friction to oppose the forces acting on it. I. The object accelerates because the force of gravity is stronger than friction.

Chapter 10 Standardized Test Prep Understanding Concepts, continued 3. For which of the following is the velocity constant? A. a baseball traveling away from a bat after a hit B. a bicyclist on an oval track moving at a constant speed of 15 km/h C. a helicopter hovering motionless above a fixed point on the ground D. a canoe being carried down a winding river by a steady current

Chapter 10 Standardized Test Prep Understanding Concepts, continued 4. When describing the motion of an object, why do you need a reference point?

Chapter 10 Standardized Test Prep Understanding Concepts, continued 4. When describing the motion of an object, why do you need a reference point? To describe the motion of an object, you need to compare the object’s position to a reference point to determine how the position is changing.

Chapter 10 Standardized Test Prep Understanding Concepts, continued 5. A jet airplane must use a substantial amount of fuel to keep flying at a constant velocity. What two forces would change the velocity of the plane if the engines were shut off?

Chapter 10 Standardized Test Prep Understanding Concepts, continued 5. A jet airplane must use a substantial amount of fuel to keep flying at a constant velocity. What two forces would change the velocity of the plane if the engines were shut off? Air resistance and the force due to gravity would change the velocity of the plane.

Chapter 10 Standardized Test Prep Reading Skills Read the passage below. Then, answer question 6. Some boats used in calm waters actually float on a cushion of air. A fan blows air below the hull of the craft, while another fan pushes air backward, propelling the boat forward. If the downward fan is turned off, the boat stops moving. The rear-facing fan cannot cause the boat to move until the other fan is turned on again.

Chapter 10 Standardized Test Prep Reading Skills, continued 6. Demonstrate why the rear-facing fan can accelerate the boat when it is on a cushion of air, but not when it is in contact with the surface of the water.

Chapter 10 Standardized Test Prep Reading Skills, continued 6. Demonstrate why the rear-facing fan can accelerate the boat when it is on a cushion of air, but not when it is in contact with the surface of the water. The boat experiences less friction when it is on a cushion of air than it does when it is in contact with the water. The rear-facing fan provides enough force to overcome only the lesser friction.

Chapter 10 Standardized Test Prep Interpreting Graphics Base you answers to questions 7 and 8 on the graph below, which shows distance (m) versus time (s).

Chapter 10 Standardized Test Prep Interpreting Graphics, continued 7. What is the average speed of the runner whose motion is plotted on the graph? F. 1.0 m/s G. 1.8 m/s H. 2.0 m/s I. 4.5 m/s

Chapter 10 Standardized Test Prep Interpreting Graphics, continued 8. During which interval is the runner’s average speed the greatest? A. 0 s to 5 s B. 5 s to 10 s C. 15 s to 20 s D. 20 s to 25 s

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