The Big Idea Santa Cruz Institute for Particle （大主意圣克鲁斯粒子研究所）.pdf

The Big Idea Acceleration is caused by force. All forces come in pairs because they arise in the interaction of two objects — you can’t hit without being hit back! The more force applied, the greater the acceleration that is produced. Objects with high masses are difficult to accelerate without a large force. In the absence of applied forces, objects simply keep moving at whatever speed they are 1 already going. In formal language : st Newton’s 1 Law: Every body continues in its state of rest, or of uniform motion in a right (straight) line, unless it is compelled to change that state by forces impressed upon it. Newton’s 2nd Law: The change of motion is proportional to the motive force impressed; and is made in the direction of the right (straight) line in which that force is impressed. Newton’s 3rd Law: To every action there is always opposed an equal reaction: or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. Key Concepts • An object will not change its state of motion (i.e., accelerate) unless an unbalanced force acts on it. Equal and oppositely directed forces do not produce acceleration. • If no unbalanced force acts on an object the object remains at constant velocity or at rest. • The force of gravity is called weight and equals mg, where g is the acceleration due to 2 gravity of the planet (g = 9.8 m/s , downward, on Earth). • Your mass does not change when you move to other planets, because mass is a measure of how much matter your body contains, and not how much gravitational force you feel. • To calculate