Motion and Mechanics Physics

Motion and Mechanics Everything in the universe moves; even if it is only very little or very slowly Motion is one part of what physicists call mechanics Forces need to act upon an object to get it moving or change its motion Velocity- how fast an object moves in a specific direction Acceleration- a measure of how much the velocity of an object changes in a certain time Mass- the amount of something there is

Forces Big- the pull of a star on a planet Small- the pull of a nucleus on an electron Gravity is a force acting on everything If there is more than one force acting on an object, the forces can be added up if they act in the same direction, or subtracted if they act in opposition. Scientists measure forces in units called Newtons

Forces A vector can be used to represent any force. A force vector describes a specific amount of force that is applied in a specific direction. If you kick that soccer ball with the same force, but in different directions, and you get different results

Gravity The force of attraction between you and the earth = weight Gravity is a force of attraction that exists between any two objects that have mass. The more mass, the greater the attraction The closer they are, the greater the force of attraction The force of attraction between you and the earth = weight Gravity is a force that should behave in similar ways regardless of where you are in the universe

Universal Law of Gravitation Every object in the universe attracts every other object with a force directed along the line of centers for the two objects that is proportional to the product of their masses and inversely proportional to the square of the separation between the two objects. G is the universal gravitational constant

Newton’s First Law An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called "the law of inertia" This means that there is a natural tendency of objects to keep on doing what they're doing. All objects resist changes in their state of motion. In the absence of an unbalanced force, an object in motion will maintain this state of motion

Newton’s Second Law Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). F=MA (Force= Mass x Acceleration) Everyone unconsciously knows the Second Law. Everyone knows that heavier objects require more force to move the same distance as lighter objects

Example Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's Second Law, you can compute how much force Mike is applying to the car F= 1,000 x 0.05 Answer= 50 Newtons

Newton’s Third Law For every action there is an equal and opposite re-action This means that for every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard