Reviewing Main Ideas 1 Newtons First Law A

Reviewing Main Ideas 1 Newton’s First Law • A force is a push or a pull. • Newton’s first law states that objects in motion tend to stay in motion and objects at rest tend to stay at rest unless acted upon by a net force. • Friction is a force that resists motion between surfaces that are touching each other.

Reviewing Main Ideas 2 Newton’s Second Law • Newton’s second law states that an object acted upon by a net force will accelerate in the direction of this force. • The acceleration due to a net force is given by the equation a = Fnet/m.

Reviewing Main Ideas 2 Newton’s Second Law • The force of gravity between two objects depends on their masses and the distance between them. • In circular motion, a force pointing toward the center of the circle acts on an object.

Reviewing Main Ideas 3 Newton’s Third Law • According to Newton’s third law, the forces two objects exert on each other are always equal but in opposite directions. • Action and reaction forces don’t cancel because they act on different objects. • Objects in orbit appear to be weightless because they are in free fall around Earth.

Chapter Review Question 1 Which of Newton’s laws explains how this rocket gets off the ground? IN: 7. 3. 17

Chapter Review Answer Newton’s third law explains how a rocket moves upward. The force of the propellant being driven out the base of the rocket causes an equal but opposite force pointing in the other direction, which drives the rocket up. IN: 7. 3. 17

Chapter Review Question 2 When the air resistance force equals a falling object’s weight, the net force on the falling object is zero. The object has reached _______. IN: 7. 3. 17

Chapter Review Answer The answer is terminal velocity. This means its acceleration is zero; it does not mean that the falling object stops moving. IN: 7. 3. 17

Chapter Review Question 3 If you are going around in circles, even at an unchanging speed, you are constantly _______. A. accelerating B. increasing in velocity C. increasing your distance D. slowing down IN: 7. 3. 17

Chapter Review Answer The answer is A. This is called circular motion. IN: 7. 3. 17

Chapter Review Question 4 When you throw a ball, why doesn’t it move in a straight line? Answer It would, if you were in space. On Earth, however, the force of gravity causes it to move in a curve as it falls. IN: 7. 3. 17

Chapter Review Question 5 What is responsible for slowing down the lunch trays in this illustration? A. acceleration B. friction C. gravity D. inertia IN: 7. 3. 17

Chapter Review Answer The answer is B. Friction always opposes sliding between two objects. IN: 7. 3. 17

Standardized Test Practice Question 1 Which would remain unchanged were you to go up in the space shuttle? A. your distance from the Earth B. your mass C. your perceptions D. your weight IN: 7. 3. 17

Standardized Test Practice Answer The answer is B. Your weight is relative to your distance from Earth and whether or not you are in freefall. IN: 7. 3. 17

Standardized Test Practice Question 2 You are swimming laps in a pool. When you come to the end, you turn around underwater and push off the wall. What does the wall do? A. it changes state B. it does nothing C. it pushes back D. it pulls on you IN: 7. 3. 17

Standardized Test Practice Answer The answer is C. Newton’s third law states that the wall pushes back on you with the same amount of force you exert on it. IN: 7. 3. 17

Standardized Test Practice Question 3 Suppose you are in a space station when suddenly you realize an asteroid is headed your way. What do you need to know about the asteroid to know how forceful the impact will be? IN: 7. 3. 17

Standardized Test Practice A. its mass B. its acceleration C. its mass and its acceleration D. its mass and its acceleration and its origin IN: 7. 3. 17

Standardized Test Practice Answer The correct answer is C. Newton showed that f =ma. If the asteroid is moving very slowly, or if it has very little mass, the force of its impact will be much less than if it is very massive and moving quickly. IN: 7. 3. 17

Standardized Test Practice Question 4 Which object would have the least acceleration if you pushed on it with a force of 5 N? A. book B. can C. cup D. stapler Object Mass (g) Cup 380 Book 1, 100 Can 240 Ruler 25 Stapler 620 IN: 7. 3. 17

Standardized Test Practice Answer The answer is A. Acceleration is calculated using the equation a = Fnet/m. IN: 7. 3. 17

Standardized Test Practice Question 5 The type of friction that prevents an object from starting to move is known as _______. A. static electrical friction B. static friction C. typical friction D. total friction IN: 7. 3. 17

Standardized Test Practice Answer The answer is B. Static friction is different from sliding friction, which slows down an object that is sliding. IN: 7. 3. 17