1. Forces and Motion

2. 12.1 Forces I. What is a force? A. The study of force is a very important part of physics. B. A push or pull that acts on an object. C. It can cause a resting object to move, or it can accelerate a moving object by changing the speed or direction. D. A spring scale is used to measure force in newtons (N).

3. E. 1 newton of force causes a1kg mass to accelerate at a rate of 1m per second each second. (1N = 1kg x m / s²) F. The newton is named after Sir Isaac Newton. G. An arrow is used to represent the direction and strength of a force. 1. The length of the arrow represents the strength or also called the magnitude of the force.

4. II. Combining Forces A. Combine force arrows to show the result of how forces combine. B. Forces in the same direction are added together. C. Forces in opposite directions are subtracted from one another. D. Net force is the overall force acting on an object when all forces are combined. E. When net force of an object is balanced, then the net force is zero and there is no change in motion. F. When unbalanced forces act on an object, the object will accelerate.

5. III. Friction A. A force that opposes the motion of objects that touch as they move past each other. B. All moving objects are subject to friction. C. There are four main types of friction. 1. Static friction – Friction force that acts on objects that are not moving. a)Always acts in the direction opposite of the applied force. 2. Sliding friction – A force that opposes the motion of an object as it slides over a surface.

6. 3. Rolling friction – A force that acts on rolling objects, caused by a change in shape at the point of rolling contact. 4. Fluid friction – The force of fluid friction opposes the motion of an object moving through a fluid. a)Liquids, gases, and lubricants are all considered fluids. b)Fluid friction acting on an object moving through the air is known as air resistance.

7. IV. Gravity A. A force that acts between any two masses. B. Is an attractive force, it pulls objects together. C. Earth’s gravity acts downward toward the center of the Earth.

8. V. Falling Objects A. Both gravity and air resistance affect the motion of a falling object. B. Gravity causes objects to accelerate downward, where as air resistance acts in the opposite direction of the motion and reduces acceleration. C. Terminal velocity is the constant velocity of a falling object when the force of air resistance equals the force of gravity.

9. VI. Projectile Motion A. The motion of a falling object after it is given an initial forward velocity. B. The combination of an initial forward velocity and the downward vertical force of gravity causes an object to follow a curved path.

10. 12.2 Newton’s First and Second Laws of Motions I. Aristotle, Galileo, and Newton A. Aristotle – An ancient Greek scientist and philosopher incorrectly proposed that force is required to keep an object moving at a constant speed. B. Galileo – An Italian scientist who concluded that moving objects not subjected to friction or any other force would continue to move indefinitely. C. Newton – Defined mass and force and introduced his laws of motion.

11. II. Newton’s First Law of Motion A. The state of motion of an object does not change as long as the net force acting on the object is zero. B. Newton’s first law of motion is sometimes called the law of inertia. C. Inertia is the tendency of an object to resist a change in its motion.

12. III. Newton’s Second Law of Motion A. The acceleration of an object is equal to the net force acting on it divided by the object’s mass. Acceleration = Net force ÷ Mass ( a = F / m) B. Mass is a measure of the inertia of an object and depends on the amount of matter the object contains. C. Newton’s 2 nd law also applies when a net force acts in an opposite direction to the object’s motion, which reduces the speed causing deceleration.

13. IV. Weight and Mass A. Weight is the force of gravity acting on an object. B. Weight = Mass x acceleration due to gravity. W = mg C. Mass is a measure of the inertia of an object. D. Weight is a measure of the force of gravity acting on an object.

14. 12-3 Newton’s Third Law of Motion and Momentum I. Newton’s Third Law A. Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. 1. These are called action and reaction forces. B. Not all action and reaction forces produce motion. C. Action and reaction forces do not cancel each other and produce a net force of zero. 1. Only when equal and opposite forces act on the same object do they result in a net force of zero.

15. II. Momentum A. The product of an object’s mass and its velocity. B. An object has a large momentum if the product of its mass and velocity is large. C. Momentum = mass x velocity. III. Conservation of Momentum A. The Law of Conservation of Momentum states, if no net force acts on a system, then the total momentum of the system does not change. B. In a closed system, the loss of momentum of one object equals the gain in momentum of another object. Momentum is conserved.

16. 12. 4 Universal Forces I. Electromagnetic Forces A. Electromagnetic forces are associated with charged particles. B. Electrocmagnetic force is the only force that can both attract and repel. C. Electric forces act between charged objects or particles such as electrons and protons. 1. Objects with opposite charges attract one another. 2. Objects with like charges repel one another. D. Magnetic forces act on certain metals, on the poles of magnets and on moving charges.

17. II. Nuclear Forces A. There are two forces that act within the nucleus to hold it together, the strong nuclear force and the weak nuclear force. B. The strong nuclear force is a powerful force of attraction that acts only on the neutrons and protons in the nucleus, holding them together.

18. III. Gravitational Force A. A force that acts between any two masses. B. Newton’s law of universal gravitation states that every object in the universe attracts every other object. 1. Gravitational force depends upon mass and distance. 2. Larger mass = larger force. 3. Greater distance = weaker force. C. Gravity is the weakest universal force, but the most effective over long distances.

19. ` D. Earth’s gravitational attraction keeps the moon in a nearly circular orbit around the Earth. E. Centripetal force is a center-directed force that continuously changes the direction of an object to make it move in a circle. F. Artificial satellites are launched into orbit by a rocket or space shuttle. 1.There are hundreds of artificial satellites orbiting Earth that perform many functions.