Class Notes

Chaps. 1-3

The fact that an object resists a change in motion is called inertia. According to Newton, the moon is held in its orbit around the earth by gravity. If we know the magnitude and direction of the net force acting on a body of given mass, Newton's second law allows us to calculate its acceleration. As a spaceship nears the moon, its mass remains. Newton's third law is a statement of the law of action-reaction. The laws of motion were formulated by Newton. The law of force is another name for Newton's second law. A change in motion can occur only if the acceleration is evidence of an unbalanced force. The speed is not a vector quantity.

The constant G is a universal constant and it is same in the whole universe. The force of gravity is inversely proportional to the square of the separation distance. Whenever an object undergoes an acceleration, a force acts upon it. The weight of a body is the force with which it is attracted to the earth. An object that has twice as much mass as another also has twice as much weight. An object of mass 25 kg acted upon by a net force of 10 N will experience an acceleration of 0.4 m/s 2 . The statement that "for every action there is an opposite but equal reaction" is regarded as Newton's third laws of motion. Acceleration refers to how fast the speed is changing.

All the systems of measurement use the same units for time. The SI system, length, mass, and time are measured in meter, kilogram, second. Give the number for the prefixes, kilo-, milli-, centi-, and deci-. What is the basic unit of volume in the metric system, liter or quart? How many ounces are present in 1.79 kg? Which of the following has the largest volume, 1 quart or 1 pint or litter ? A sprinter runs the 1 km dash in 9.8 seconds. What is the average speed? ( answer is 102 m/s). A bicycle starts from rest and reaches 10.0 m/s after 5.0 seconds. What is its acceleration? ( answer is 2 m/s.s). A car that is traveling with a constant speed has zero acceleration. The speedometer of a car indicates instantaneous speed. For an object in free fall, the velocity changes uniformly with time. Motion is a process of a change in position. 43. If the speed of a moving car is 100 mi/h, how far will it travel in 5 hours? How long does it take a stone to fall 1km starting from rest?
Note: Do the Home Work. May the net force be with you!!