universal laws of physics

• Laws of nature as expressed in physics as laws and theories are often said to be universal
• This means that, so far as we have been able to test them, they apply everywhere and at every time, past, present and future
• Mechanics


  The study of motion or movement of the object(s)
• Motion


  An object's change in position with respect to time
• Kinematics


  Description of motion
• Aristotle's view of motion

  • Natural motion - any motion that an object does naturally without being forced
  • Violent motion - an object will move if an external force such as pushing or pulling is applied to it
• Galileo's view of motion

  • Bodies fall on the surface of the earth at a constant acceleration
  • The force of gravity which causes all bodies to move downward is a constant force
  • A free-falling object is an object that is falling under the sole influence of gravity
• Aristotle's view of vertical motion

  The element earth moves down towards its natural resting place, air rises to its natural place in the atmosphere, fire leaps upward to its natural place above the atmosphere, water's natural place is just above the earth
• Aristotle's view of horizontal motion

  Bodies need to be pushed or pulled to maintain horizontal motion
• Galileo's view of horizontal motion

  If there is no interference, a moving object will keep moving in a straight line forever, there is no need to push, pull or apply force of any kind
• Aristotle's view of projectile motion

  An object is influenced by the downward force of gravity, projectiles follow a curved path
• Galileo's view of projectile motion

  Projectile motion could be understood by analyzing the horizontal and vertical components separately
• Inertia


  The property of an object to resist changes in motion
• Law of inertia


  • With no net force acting upon it, an object at rest tends to stay at rest, and an object in motion tends to stay in motion, both objects will continue with the same inertia, keeping the same velocity
• When a car is brought to an abrupt stop

  Its passengers possess inertia which tries to resist this sudden deceleration
• Law of acceleration


  The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object
• Calculating force, acceleration, and mass


  • Example 1: What resultant force is required to give 8 kg block an acceleration of 3 m/s2?
  • Example 2: A bobsleigh of mass 500 kg is pushed at the start with a force of 2000N. What is its initial acceleration?
  • Example 3: A toy car accelerates at 2 m/s2 with a constant force of 10 N. What is the mass of the car?
• Law of action and interaction


  For every action, there is an equal and opposite reaction
• Examples of action and reaction

  • A rocket ship launched into air pushes gases out its rear which in turn pushes the rocket forward
  • The wheels of a vehicle actually spin backward and the road reacts by pushing the wheels forward
  • A bird flies by use of its wings, the wings of a bird push air downwards and the air must also be pushing the birds upwards
• Newton's law of universal gravitation


  Gravity is a force that should behave in similar ways regardless of where you are in the universe, all objects attract each other with a force of gravitational attraction
• Gravity


  A force of attraction that exists between any two objects that have mass, the more mass they have, the greater the force of attraction, the closer they are, the greater the force of attraction
• Gravity is a very weak force, so between common objects like you and your ballpen, the force of attraction is very small because your mass and the mass of your ballpen is small
• Weight


  The force of attraction between you and the Earth
• Newton's law of universal gravitation guides the efforts of scientists in their study of planetary orbits, it can explain the small perturbations in a planet's elliptical motion
• Newton's ability to relate the cause for heavenly motion (the orbit of the moon about the earth) to the cause for Earthly motion (the fall of an apple to the Earth) led him to his notion of universal gravitation