Measuring Force You may have measured forces using a spring scale. The of the spring in the scale depends on the amount of (a type of ) acting on it.

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1 Forces 12.1 Name 1 A is a push or a pull that on an. How do forces affect the motion of an object? Measuring Force You may have measured forces using a spring scale. The of the spring in the scale depends on the amount of (a type of ) acting on it. Units of Force One (N) is the force that causes a 1-kilogram mass to accelerate at a of 1 meter per each second (1 m/s 2 ). 1 N = When the forces on an object are balanced, the net force is, and there is no change in the object s. When an force acts on an object, the object. Representing Force can represent a force. The of the arrows show relative of force. Free-body diagrams are diagrams used to show the forces acting upon an object in a given situation. The net force is the force acting on an after the forces are Forces in the same direction together. Forces in directions from one another. Balanced Forces Balanced forces are forces that to produce a net force of. An unlimited number of individual forces can act on an object to produce a net force of zero. The two groups with equal forces in directions. The forces to make a net force of. Unbalanced Forces An force is a force that results when the force acting on an object is equal to zero. Forces can add together or subtract from one another.

2 2 Static Friction Static friction is the friction force that acts on objects that are moving. Static friction acts in the direction to that of the force. Sliding Friction Sliding friction is a force that the of motion of an object as it over a surface. Sliding friction is than static friction. Static friction the potted tree does not move. Sliding friction when the tree moves, sliding friction acts to oppose the direction of motion. Rolling Friction Rolling friction is the friction force that acts on objects. The force of friction is about 100 to 1000 times than the force of static or sliding friction. Ball in these wheels greatly reduce friction by sliding with rolling friction. Fluid Friction Fluid friction the motion of an object through a. Fluid friction acting on an object moving through the air is known as. Fluid friction as the of the object moving through the fluid. Gravity is a that acts between two masses. Gravity is Gravity can Earth exerts an, downward force on this. The supporting rock exerts an force on the boulder. The forces are. Falling Objects Both gravity and air resistance affect the. As objects fall to the ground, they is the velocity of a falling object when the force of air resistance the force of gravity. This flying squirrel takes advantage of air resistance to slow its fall and increase the distance covered in the jump. A thrown ball follows a path.

3 Projectile motion is the of a falling object (projectile) it is given an velocity. Air resistance and are the only forces acting on a Quiz Questions 1. If an object is at rest, which of the following statements is most likely true? A) There are no forces acting on the object. B) There is no friction acting on the object. C) The forces acting on the object are unbalanced. D) The net force acting on the object is zero. 2.Which of the following is not a type of friction? A) static friction B) sliding friction C) fluid friction D) pull friction 3. In which direction does Earth s gravitational force act? A) opposite the direction of motion B) downward toward the center of Earth C) upward away from the center of Earth D) in the direction of motion 4. A ball thrown into the air follows a projectile course due to the initial velocity and the A) force of gravity. B) effect of air resistance. C) motion of Earth beneath it. D) mass of the ball. 5. What is the SI unit for force? A) kepler B) newton C) galileo D) bohr

4 Newton s 1 st and 2 nd Aristotle Aristotle made scientific discoveries through careful and reasoning. Aristotle proposed that is required to keep an object at speed. Galileo Galileo Galilei studied how produces acceleration. He rolled balls down wooden ramps. He concluded that moving objects would continue to move indefinitely. to friction or any other Newton built on the work of scientists such as Galileo. Newton first defined mass and force. He then introduced his of motion. According to Newton s law of motion, the state of motion of an object does not change as long as the force acting on the object is zero. Unless an force acts, an object at rest at rest. Unless an unbalanced force acts, an object in remains in motion with the same and. is the tendency of an object to a in its. This crash sequence illustrates. The test dummy continues its forward motion as the car slows and stops. According to Newton s law of motion, the acceleration of an object is to the net acting on it divided by the object s. (write formula here) The acceleration of an object is proportional to the net force acting on it. The of an object also depends upon its. is a measure of the of an object.

5 The acceleration of an object is in the same as the net force. When a net force acts in the direction to the object s, the force produces a. 5 Newton s Second Law An automobile with a mass of 1000 kilograms accelerates when the traffic light turns green. If the net force on the car is 4000 newtons, what is the car s acceleration? What unknown are you trying to calculate? What formula contains the given quantities and the unknown? Replace each variable with its known value and solve. 1. A boy pushes forward a cart of groceries with a total mass of 40.0 kg. What is the acceleration of the cart if the net force on the cart is 60.0 N? 2. What is the upward acceleration of a helicopter with a mass of 5000 kg if a force of 10,000 N acts on it in an upward direction? 3. An automobile with a mass of 1200 kg accelerates at a rate of 3.0 m/s 2 in the forward direction. What is the net force acting on the automobile? (Hint: Solve the acceleration formula for force.) 4. A 25-N force accelerates a boy in a wheelchair at 0.5 m/s2. What is the mass of the boy and the wheelchair? (Hint: Solve Newton s second law for mass.)

6 Acceleration depends directly on force and on mass. The same force causes the single cart to accelerate times faster than the chain of carts. 6 Mass and weight are related but are the. Mass is the of the of an object contains. is the force of gravity on an object. Weight is the of mass and due to gravity. W = mg is a different form of Newton s Second Law, F = ma. The value of g in the formula is 9.8 m/s 2. If an astronaut has a mass of 112 kilograms, what is his weight on Earth where the acceleration due to gravity is 9.8 m/s 2? Weight = Mass Acceleration due to gravity On the moon, the acceleration due to is only about one that on Earth. The astronaut weighs only about one as much on the moon as on Earth. The of the astronaut is the on the moon and on Earth. 1. What is inertia? A) the force of gravity acting on an object B) forces of friction slowing an object s motion C) the mass of an object D) the tendency of an object to resist change in its motion 3. A plane with a mass of 5,000 kg accelerates at a rate of 100 m/s 2. What is the force produced by the jet engines? A) 500,000 N B) 50N C) 100,000 N D) 5,000 N 2.A 3600-N force causes a car to accelerate at a rate of 4 m/s 2. What is the mass of the car? A) 600 kg B) 900 kg C) 14,400 kg D) 1200 kg 4. How would your mass and weight change if you were on the moon s surface? A) They wouldn t change. B) Your mass would remain constant, and your weight would increase. C) Your mass and weight would decrease. D) Your mass would remain constant, and your weight would decrease.

7 Newton s 3 rd Law 12.3 When this bumper car with another car, two forces are exerted. Each car in the exerts a on the other. According to Newton s law of motion, whenever one object a force on a object, the second object exerts an and force on the first object. 7 Action and Reaction Forces The force your bumper car exerts on the other car is the force. The force the other car exerts on your car is the force. These two forces are in size and in direction. Suppose you press your hand against a wall. Your hand exerts an force on the wall. The wall exerts an equal and opposite reaction against your hand. Action-Reaction Forces and Motion A swimmer pushing the water is an action force. The force acting on the swimmer causes through the water. Action-Reaction Forces Do Not Cancel For the swimmer, why do the and forces not cancel each other and produce a net force of? The action and reaction forces act on the object. is the product of an object s and its. Momentum formula: An object with momentum is to stop than an object with momentum. The momentum for any object at rest is. Mass is measured in. Velocity is measured in per second. Momentum is measured kilogram-meters per second.

8 8 Which has more momentum, a kilogram golf ball with a speed of 60.0 meters per second, or a 7.0- kilogram bowling ball with a speed of 6.0 meters per second? How is momentum conserved? Objects within a system can exert forces on one. A closed system means other objects and forces enter or a system. According to the law of conservation of, if no net force acts on a system, then the total momentum of the system change. In each collision, the total momentum of the train cars does not change momentum is conserved. 1. A stationary figure skater pushes off the boards around an ice skating rink and begins gliding backward, away from the boards. Which law explains why the figure skater moves backward? A) the law of conservation of energy B) the law of inertia C) Newton s second law D) Newton s third law 2. A red puck with Velcro on its side is sliding toward a stationary blue Velcro puck of the same mass. The pucks will stick together upon contact. After contact, how will the red puck s velocity compare to its initial velocity? (In this collision the law of conservation of momentum is obeyed, and friction is ignored.) A) The red puck s velocity is the same as before. B) The red puck s velocity is the same magnitude but in the opposite direction. C) The red puck s velocity is half its initial velocity and in the same direction. D) The red puck s velocity is double its initial velocity and in the opposite direction. Universal Forces 12.4 Observations of, stars, and strongly suggest four universal forces exist throughout the universe. Electro nuclear Weak

9 9 forces act over a between particles of. The particles be in. Force is affected by the between particles. What force can attract and repel? Electric and magnetic force are two different aspects of the force. Electromagnetic force is with particles. Electric forces act between objects or. Objects with charges attract one another. Objects with like charges one another. Clothes often acquire electric in the dryer. Clothes with charges tend to cling together. Magnetic Forces Magnetic forces act on certain, the of magnets, and moving. Magnets have two poles north and south. Two poles that are opposite each other. Two poles that are repel each other. The strong nuclear force the electric force of that acts among the in the nucleus. The weak nuclear force is involved in certain types of processes. Strong Nuclear Force The strong nuclear force is a powerful force of attraction that acts only on the and in the. It acts over short distances approximately the diameter of a (10 15 m). It is times stronger than the force of repulsion at these distances.

10 Weak Nuclear Force The nuclear force is an force that acts only over a range. The weak nuclear force acts at about meters, less than the range of the nuclear force. What is Newton s law of universal gravitation? 10 Gravitational force is an attractive force that acts between any two masses. Gravitational force depends upon and. The gravitational force between objects is to their. Gravitational force with the square of the between the objects. Gravity is the universal force, but it is the most effective force over long. The Earth, Moon, and Tides The moon s acts to move it away from. Earth s gravitational keeps the moon in a nearly orbit around Earth. A centripetal force is a center-directed that continuously the direction of an object to make it move in a. The moon s inertia and the gravitational pull of Earth result in a nearly circular orbit. The gravitational pull from the moon produces two bulges in Earth s one on the side of Earth to the moon, the other on the side from the moon. As Earth rotates per beneath these two bulges, there are two and two tides per day on Earth. Satellites in Orbit An artificial satellite needs only its and the force provided by gravity to maintain its orbit. Satellites in a low orbit are slowed by friction with Earth s atmosphere and eventually reenter Earth s atmosphere.

11 Uses of Satellites Hundreds of artificial satellites orbit for many functions: monitoring Earth s weather creating detailed radar maps of Earth s surface using telescopes to study space studying Earth s climate receiving and transmitting radio and microwave signals 11 Satellites are used to receive and transmit electromagnetic waves over great distances. 1. What are the only forces that can both attract and repel? A) electromagnetic forces B) centripetal forces C) strong nuclear forces D) gravitational forces 2. The nucleus of an atom is held together primarily by the A) strong force and weak force. B) strong force and gravity. C) weak force and electromagnetic force. D) electromagnetic force and strong force. 3. Which of the following statements about gravitational forces is false? A) They are the weakest universal forces. B) They act between any two objects. C) They become stronger as the distance between two objects increases. D) They become weaker as the mass of either two objects decreases. 4. Gravitational force depends on what two things? A) Force and distance B) Distance and mass C) Mass and acceleration D) Inertia and velocity