A chandelier hangs from a chain in the middle of a dining

What is a force?

How do we identify forces?

How do we show forces?

What do forces do?

What is Newtons first law?

What good are forces?

What is a force?

What is the connection between force and motion?

A bungee jumper has leapt off a bridge and is nearing the bottom of her fall. What forces are being exerted on the jumper?

A skier is being towed up a snow-covered hill by a tow rope. What forces are being exerted on the skier?

Youve just kicked a rock, and it is now sliding across the ground 2 m in front of you. Which of these forces act on the rock? List all that apply. a. Gravity, acting downward. b. The normal force, acting upward. c. The force of the kick, acting in the direction of motion. d. Friction, acting opposite the direction of motion

A rocket is being launched to place a new satellite in orbit. Air resistance is not negligible. What forces are being exerted on the rocket?

Two rubber bands stretched to the standard length cause an object to accelerate at 2 m/s2 . Suppose another object with twice the mass is pulled by four rubber bands stretched to the standard length. The acceleration of this second object is a. 1 m/s2 b. 2 m/s2 c. 4 m/s2 d. 8 m/s2 e. 16 m/s2

What Do Forces Do?

Three forces act on an object. In which direction does the object accelerate?

An elevator, suspended by a cable, speeds up as it moves upward from the ground floor. Identify the forces and draw a free-body diagram of the elevator.

Bobby straps a small model rocket to a block of ice and shoots it across the smooth surface of a frozen lake. Friction is negligible. Draw a pictorial representation of the block of ice.

An elevator suspended by a cable is moving upward and slowing to a stop. Which free-body diagram is correct? T T u u T u y x y x y

What Good Is Newtons First Law?

A tow rope pulls a skier up a snow-covered hill at a constant speed. Draw a pictorial representation of the skier.

An elevator suspended by a cable is descending at constant velocity. How many force vectors would be shown on a free-body diagram? Name them.

A compressed spring is pushing a block across a rough horizontal table. How many force vectors would be shown on a free-body diagram? Name them.

A brick is falling from the roof of a three-story building. How many force vectors would be shown on a free-body diagram? Name them

In FIGURE Q5.4, block B is falling and dragging block A across a table. How many force vectors would be shown on a free-body diagram of block A? Name them.

You toss a ball straight up in the air. Immediately after you let go of it, what force or forces are acting on the ball? For each force you name, (a) state whether it is a contact force or a long-range force and (b) identify the agent of the force

A constant force applied to A causes A to accelerate at 5 m/s2 . The same force applied to B causes an acceleration of 3 m/s2 . Applied to C, it causes an acceleration of 8 m/s2 . a. Which object has the largest mass? Explain. b. Which object has the smallest mass? c. What is the ratio mA/mB of the mass of A to the mass of B?

An object experiencing a constant force accelerates at 10 m/s2 . What will the acceleration of this object be if a. The force is doubled? Explain. b. The mass is doubled? c. The force is doubled and the mass is doubled?

An object experiencing a constant force accelerates at 8 m/s2 . What will the acceleration of this object be if a. The force is halved? Explain. b. The mass is halved? c. The force is halved and the mass is halved?

If an object is at rest, can you conclude that there are no forces acting on it? Explain.

If a force is exerted on an object, is it possible for that object to be moving with constant velocity? Explain

Is the statement An object always moves in the direction of the net force acting on it true or false? Explain

Newtons second law says F u net = mau . So is mau a force? Explain

Is it possible for the friction force on an object to be in the direction of motion? If so, give an example. If not, why not?

Suppose you press your physics book against a wall hard enough to keep it from moving. Does the friction force on the book point (a) into the wall, (b) out of the wall, (c) up, (d) down, or (e) is there no friction force? Explain.

FIGURE Q5.15 shows a hollow tube forming three-quarters of a circle. It is lying flat on a table. A ball is shot through the tube at high speed. As the ball emerges from the other end, does it follow path A, path B, or path C? Explain.

Which, if either, of the basketballs in FIGURE Q5.16 are in equilibrium? Explain

Which of the following are inertial reference frames? Explain. a. A car driving at steady speed on a straight and level road. b. A car driving at steady speed up a 10 incline. c. A car speeding up after leaving a stop sign. d. A car driving at steady speed around a curve

A car is parked on a steep hill. Identify the forces on the car

A chandelier hangs from a chain in the middle of a dining room. Identify the forces on the chandelier.

A baseball player is sliding into second base. Identify the forces on the baseball player

A jet plane is speeding down the runway during takeoff. Air resistance is not negligible. Identify the forces on the jet

An arrow has just been shot from a bow and is now traveling horizontally. Air resistance is not negligible. Identify the forces on the arrow.

Two rubber bands cause an object to accelerate with acceleration a. How many rubber bands are needed to cause an object with half the mass to accelerate three times as quickly?

Two rubber bands pulling on an object cause it to accelerate at 1.2 m/s2 . a. What will be the objects acceleration if it is pulled by four rubber bands? b. What will be the acceleration of two of these objects glued together if they are pulled by two rubber bands?

FIGURE EX5.8 shows acceleration-versus-force graphs for two objects pulled by rubber bands. What is the mass ratio m1/m2?

FIGURE EX5.9 shows an acceleration-versus-force graph for three objects pulled by rubber bands. The mass of object 2 is 0.20 kg. What are the masses of objects 1 and 3? Explain your reasoning.

For an object starting from rest and accelerating with constant acceleration, distance traveled is proportional to the square of the time. If an object travels 2.0 furlongs in the first 2.0 s, how far will it travel in the first 4.0 s?

Youll learn in Chapter 25 that the potential energy of two electric charges is inversely proportional to the distance between them. Two charges 30 nm apart have 1.0 J of potential energy. What is their potential energy if they are 20 nm apart?

FIGURE EX5.12 shows an acceleration-versus-force graph for a 200 g object. What force values go in the blanks on the horizontal scale?

FIGURE EX5.13 shows an acceleration-versus-force graph for a 500 g object. What acceleration values go in the blanks on the vertical scale?

FIGURE EX5.14 shows the acceleration of objects of different mass that experience the same force. What is the magnitude of the force?

FIGURE EX5.15 shows an objects acceleration-versus-force graph. What is the objects mass?

Based on the information in Table 5.1, estimate a. The weight of a laptop computer. b. The propulsion force of a bicycle.

Exercises 17 through 19 show two of the three forces acting on an object in equilibrium. Redraw the diagram, showing all three forces. Label the third force F u 3

Exercises 17 through 19 show two of the three forces acting on an object in equilibrium. Redraw the diagram, showing all three forces. Label the third force F u 3

Exercises 17 through 19 show two of the three forces acting on an object in equilibrium. Redraw the diagram, showing all three forces. Label the third force F u 3

Exercises 20 through 22 show a free-body diagram. For each, write a short description of a real object for which this would be the correct free-body diagram. Use Examples 5.4, 5.5, and 5.6 as examples of what a description should be like

Exercises 20 through 22 show a free-body diagram. For each, write a short description of a real object for which this would be the correct free-body diagram. Use Examples 5.4, 5.5, and 5.6 as examples of what a description should be like

Exercises 20 through 22 show a free-body diagram. For each, write a short description of a real object for which this would be the correct free-body diagram. Use Examples 5.4, 5.5, and 5.6 as examples of what a description should be like

Exercises 23 through 27 describe a situation. For each, identify all forces acting on the object and draw a free-body diagram of the object.A cat is sitting on a window sill.

Exercises 23 through 27 describe a situation. For each, identify all forces acting on the object and draw a free-body diagram of the object.An ice hockey puck glides across frictionless ice.

Exercises 23 through 27 describe a situation. For each, identify all forces acting on the object and draw a free-body diagram of the object.Your physics textbook is sliding across the table

Exercises 23 through 27 describe a situation. For each, identify all forces acting on the object and draw a free-body diagram of the object.A steel beam, suspended by a single cable, is being lowered by a crane at a steadily decreasing speed.

Exercises 23 through 27 describe a situation. For each, identify all forces acting on the object and draw a free-body diagram of the object.A jet plane is accelerating down the runway during takeoff. Friction is negligible, but air resistance is not.

Redraw the two motion diagrams shown in FIGURE P5.28, then draw a vector beside each one to show the direction of the net force acting on the object. Explain your reasoning.

A single force with x-component Fx acts on a 2.0 kg object as it moves along the x-axis. The objects acceleration graph (ax versus t) is shown in FIGURE P5.29. Draw a graph of Fx versus t.

A single force with x-component Fx acts on a 500 g object as it moves along the x-axis. The objects acceleration graph (ax versus t) is shown in FIGURE P5.30. Draw a graph of Fx versus t.

A single force with x-component Fx acts on a 2.0 kg object as it moves along the x-axis. A graph of Fx versus t is shown in FIGURE P5.31. Draw an acceleration graph (ax versus t) for this object.

A single force with x-component Fx acts on a 500 g object as it moves along the x-axis. A graph of Fx versus t is shown in FIGURE P5.32. Draw an acceleration graph (ax versus t) for this object

A constant force is applied to an object, causing the object to accelerate at 8.0 m/s2 . What will the acceleration be if a. The force is doubled? b. The objects mass is doubled? c. The force and the objects mass are both doubled? d. The force is doubled and the objects mass is halved?

A constant force is applied to an object, causing the object to accelerate at 10 m/s2 . What will the acceleration be if a. The force is halved? b. The objects mass is halved? c. The force and the objects mass are both halved? d. The force is halved and the objects mass is doubled?

Problems 35 through 40 show a free-body diagram. For each: a. Identify the direction of the acceleration vector a u and show it as a vector next to your diagram. Or, if appropriate, write a u = 0 u . b. If possible, identify the direction of the velocity vector v u and show it as a labeled vector. c. Write a short description of a real object for which this is the correct free-body diagram. Use Examples 5.4, 5.5, and 5.6 as models of what a description should be like

Problems 35 through 40 show a free-body diagram. For each: a. Identify the direction of the acceleration vector a u and show it as a vector next to your diagram. Or, if appropriate, write a u = 0 u . b. If possible, identify the direction of the velocity vector v u and show it as a labeled vector. c. Write a short description of a real object for which this is the correct free-body diagram. Use Examples 5.4, 5.5, and 5.6 as models of what a description should be like

Problems 35 through 40 show a free-body diagram. For each: a. Identify the direction of the acceleration vector a u and show it as a vector next to your diagram. Or, if appropriate, write a u = 0 u . b. If possible, identify the direction of the velocity vector v u and show it as a labeled vector. c. Write a short description of a real object for which this is the correct free-body diagram. Use Examples 5.4, 5.5, and 5.6 as models of what a description should be like

Problems 35 through 40 show a free-body diagram. For each: a. Identify the direction of the acceleration vector a u and show it as a vector next to your diagram. Or, if appropriate, write a u = 0 u . b. If possible, identify the direction of the velocity vector v u and show it as a labeled vector. c. Write a short description of a real object for which this is the correct free-body diagram. Use Examples 5.4, 5.5, and 5.6 as models of what a description should be like

Problems 35 through 40 show a free-body diagram. For each: a. Identify the direction of the acceleration vector a u and show it as a vector next to your diagram. Or, if appropriate, write a u = 0 u . b. If possible, identify the direction of the velocity vector v u and show it as a labeled vector. c. Write a short description of a real object for which this is the correct free-body diagram. Use Examples 5.4, 5.5, and 5.6 as models of what a description should be like

Problems 35 through 40 show a free-body diagram. For each: a. Identify the direction of the acceleration vector a u and show it as a vector next to your diagram. Or, if appropriate, write a u = 0 u . b. If possible, identify the direction of the velocity vector v u and show it as a labeled vector. c. Write a short description of a real object for which this is the correct free-body diagram. Use Examples 5.4, 5.5, and 5.6 as models of what a description should be like

In lab, you propel a cart with four known forces while using an ultrasonic motion detector to measure the carts acceleration. Your data are as follows: Force 1N2 Acceleration 1m/s2 2 0.25 0.5 0.50 0.8 0.75 1.3 1.00 1.8 a. How should you graph these data so as to determine the mass of the cart from the slope of the line? That is, what values should you graph on the horizontal axis and what on the vertical axis? b. Is there another data point that would be reasonable to add, even though you made no measurements? If so, what is it? c. What is your best determination of the carts mass?

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram An elevator, suspended by a single cable, has just left the tenth floor and is speeding up as it descends toward the ground floor

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram A rocket is being launched straight up. Air resistance is not negligible.

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram A Styrofoam ball has just been shot straight up. Air resistance is not negligible

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram You are a rock climber going upward at a steady pace on a vertical wall.

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram Youve slammed on the brakes and your car is skidding to a stop while going down a 20 hill.

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram Youve just kicked a rock on the sidewalk and it is now sliding along the concrete

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram Youve jumped down from a platform. Your feet are touching the ground and your knees are flexing as you stop

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram You are bungee jumping from a high bridge. You are moving downward while the bungee cord is stretching.

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram Your friend went for a loop-the-loop ride at the amusement park. Her car is upside down at the top of the loop.

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram A spring-loaded gun shoots a plastic ball. The trigger has just been pulled and the ball is starting to move down the barrel. The barrel is horizontal

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram A person on a bridge throws a rock straight down toward the water. The rock has just been released.

The leaf hopper, champion jumper of the insect world, can jump straight up at 4 m/s2 . The jump itself lasts a mere 1 ms before the insect is clear of the ground. a. Draw a free-body diagram of this mighty leaper while the jump is taking place. b. While the jump is taking place, is the force of the ground on the leaf hopper greater than, less than, or equal to the force of gravity on the leaf hopper? Explain

A bag of groceries is on the seat of your car as you stop for a stop light. The bag does not slide. Draw a motion diagram, a force-identification diagram, and a free-body diagram for the bag.

A heavy box is in the back of a truck. The truck is accelerating to the right. Draw a motion diagram, a force-identification diagram, and a free-body diagram for the box

If a car stops suddenly, you feel thrown forward. Wed like to understand what happens to the passengers as a car stops.Imagine yourself sitting on a very slippery bench inside a car. This bench has no friction, no seat back, and theres nothing for you to hold onto. a. Draw a picture and identify all of the forces acting on you as the car travels at a perfectly steady speed on level ground. b. Draw your free-body diagram. Is there a net force on you? If so, in which direction? c. Repeat parts a and b with the car slowing down. d. Describe what happens to you as the car slows down. e. Use Newtons laws to explain why you seem to be thrown forward as the car stops. Is there really a force pushing you forward? f. Suppose now that the bench is not slippery. As the car slows down, you stay on the bench and dont slide off. What force is responsible for your deceleration? In which direction does this force point? Include a free-body diagram as part of your answer

A rubber ball bounces. Wed like to understand how the ball bounces. a. A rubber ball has been dropped and is bouncing off the floor. Draw a motion diagram of the ball during the brief time interval that it is in contact with the floor. Show 4 or 5 frames as the ball compresses, then another 4 or 5 frames as it expands. What is the direction of a u during each of these parts of the motion? b. Draw a picture of the ball in contact with the floor and identify all forces acting on the ball. c. Draw a free-body diagram of the ball during its contact with the ground. Is there a net force acting on the ball? If so, in which direction? d. Write a paragraph in which you describe what you learned from parts a to c and in which you answer the question: How does a ball bounce?