chapter 4 dynamics

• a force is a push or pull on an object that causes it to change its motion.
• SI unit of force: Newton (N)

  measured with a forcemeter (spring balance)
• Newton's First Law of motion

  every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it
• Fist law is known as Law of Inertia
• Inertia

  reluctance of the object to change its state of rest or motion, due to its mass
• the greater the mass the greater its inertia
• when an object has no resultant force, we say that the forces are balanced and therefore is at rest or moving at a constant speed
• Newton's Second Law of Motion

  when a resultant force acts on an object of a constant mass, the object will accelerate in the direction of the resultant force
• formula of resultant force

  Fnet = m x a

  Fnet = force/unbalanced force/resultant force (N)

  m = mass (kg)

  a = acceleration (m/s2)
• Friction

  is a contact force that opposes motion
• factors affecting friction

  type of material/surface

  mass
• advantages of friction

  walk without slipping

  moving objects are able to slow down when needed
• disadvantages of friction

  wear and tear

  cars lose efficiency by up to 20%
• ways to reduce friction

  wheels, ball bearings, lubricants
• Newton's third law of motion

  if Body a exerts a force F on body B, body B will exert an equal and opposite force F on body A
• action and reaction

  forces always occur in pairs

  the 2 forces are equal in magnitude

  forces act in opposite directions

  forces act on different bodies