FIG. 2-1 A car whose average speed is 40 miles/hour travels 240 miles in 6 hours.

FIG. 2-2 There are 1000 meters in a kilometer and 100 centimeters in a meter.

FIG. 2-3 The vector v represents a velocity of 40 km/s to the right. The scale is 1 cm = 10 km/h.

FIG. 2-4Adding vector B (3km east) to vector A (5 km north) gives vector C whose length corresponds to 5.8 km.

FIG. 2-5 Three cases of accelerated motion, showing successive positions of a body after equal periods of time. At the top the intervals between the positions of the body increase in length because the body is traveling faster and faster. Below it the intervals decrease in length because the body is slowing down. At the bottom the intervals are the same in length because the speed is constant, but the direction of motion is constantly changing.

FIG. 2-7 Falling bodies are accelerated downward. A stone dropped from a height of 5 m strikes the ground with a speed more than double that of a stone dropped from a height of 1 m.

FIG. 2-8 All falling objects have a downward acceleration of 9.8 m/s². (The distance an object will have fallen in each time interval is not shown to scale here.)

FIG. 2-9 The acceleration of gravity does not depend upon horizontal motion. When one ball is thrown horizontally from a building at the same time that a second ball is dropped vertically, the two reach the ground at the same time because both have the same downward acceleration.

FIG. 2-10 When a ball is thrown upward, its downward acceleration reduces its original speed until it comes to a momentary stop. At this time the ball is at the top of its path, and it then begins to fall as if it had been dropped from there. The ball is shown after equal time intervals.

FIG. 2-11In the absence of air resistance, a ball travels farthest when it is thrown at an angle of 45° .

FIG. 2-12 In a vacuum all bodies fall with the same acceleration.

FIG. 2-13 Effect of air resistance on the path of a thrown ball. An angle of less than 45° now gives the greatest range.

FIG. 2-14 When several forces act on an object, they may cancel one another out to leave no net force. Only a net (or unbalanced) force can accelerate an object.

FIG. 2-15 When a car suddenly starts to move, the inertia of the passengers tends to keep them at rest relative to the earth, and so their heads move backward relative to the car. (b) When the car comes to a sudden stop, inertia tends to keep the passengers moving, and so their heads move forward relative to the car.

FIG. 2-16 A liter, which is equal to 1.057 quarts, represents a volume of 1000 cubic centimeters (cm³). One liter of water has a mass of 1 kg.

FIG. 2-17 Newton's second law of motion. When different forces act upon the same mass, the greater force produces the greater acceleration. When the same force acts upon different masses, the greater mass receives the smaller acceleration.

FIG. 2-18 The direction of a force is significant. A force applied in the direction in which a body is moving produces a positive acceleration (increase in speed). A force applied opposite to the direction of motion produces a negative acceleration (decrease in speed).

FIG. 2-20 A person serving a tennis ball must exert a force of 360 N on it for the ball to have a speed of 30 m/s if the racket is in contact with the ball for 0.005 s.

FIG. 2-21 Action and reaction forces act on different bodies. Pushing a table on a frozen lake results in person and table moving apart in opposite directions.

FIG. 2-22 Some examples of action-reaction pairs of forces.

FIG. 2-24 The centripetal force needed to keep an object moving in a circle depends upon the mass and speed of the object and upon the radius of the circle. The direction of the force is always toward the center of the circle.

FIG. 2-25 A centripetal force of 833 N is needed by this car to make the turn shown.

FIG. 2-26 The gravitational force between two bodies depends upon the square of the distance between them. The gravitational force on a planet would drop to one-fourth its usual amount if the distance of the planet from the sun were to be doubled. If the distance is halved, the force would increase to 4 times its usual amount.

FIG. 2-27 For computing gravitational effects, spherical bodies (such as the earth and moon) may be regarded as though their masses are located at their geometrical centers, provided that they are uniform spheres or consist of concentric uniform spherical shells.

FIG. 2-28 The weight of a person near the earth is the gravitational force the earth exerts upon her. As she goes farther and farther away from the earth's surface, her weight decreases inversely as the square of her distance from the earth's center. The mass of the person here is 60 kg.

FIG. 2-29 The gravitational force of the earth on an apple at the earth's surface is the same as the force between masses M and m the distance R apart. This force equals the weight of the apple.

FIG. 2-30 In the Global Positioning System (GPS), each of a fleet of orbiting satellites sends out coded radio signals that enable a receiver on the earth to determine both the exact position of the satellite in space and its exact distance from the receiver. Given this information, a computer in the receiver then calculates the circle on the earth's surface on which the receiver must lie. Data from three satellites give three circles, and the receiver must be located at the one point where all three intersect.

FIG. 2-31 The minimum speed an earth satellite can have is 28,400 km/h. The escape speed from the earth is 40,000 km/h.