Science-8

• Experiences of riding a car


  • Car exhilarates abruptly, making you feel as if your body is pulled to the back
  • Driver suddenly steps on the brakes, and you feel the seat belt tighten
• Newton's first law of motion

  The law of inertia, which explains how an object responds to changes in motion
• Force


  Any push or pull that causes changes in the motion of an object
• Types of force


  • Contact force
  • Non-contact force
• Contact force


  Present when two or more surfaces or media touch and interact
• Friction


  A specific type of contact force, the object's resistance to motion
• Non-contact force


  Constantly present in nature and does not need human intervention to arise
• Non-contact force


  • The sun and planets exerting a gravitational pull on each other despite their large spatial separation
• Aspects of motion


  • Speed
  • Velocity
  • Acceleration
• Speed


  The length of distance traveled in a certain amount of time
• Velocity


  The rate of change of displacement of an object
• Acceleration


  The rate of change of velocity of an object
• Motion examples


  • Car going 100 miles per hour (speed)
  • Car going 100 miles per hour east (velocity)
  • Car slowing down at the stop sign, then speeding up (acceleration)
• Newton's first law of motion


  The response of an object to changes in motion
• Parts of Newton's first law of motion

  • An object at rest will remain at rest unless acted on by an unbalanced force
  • An object in motion continues to move with the same velocity unless acted on by an imbalanced force
• Inertia


  The property that resists the changes in an object, independent from external force and mass-dependent
• Inertia examples


  • Box at rest, acted upon by normal force and gravitational force (balanced forces)
  • Spacecraft in space, with engines turned off (constant speed and direction)
  • Riding a car, experiencing sudden stop (inertia keeps you moving)
• Activity with coin, glass, and cardboard

  1. Arrange setup, slowly pull cardboard

  2. Arrange setup, quickly flick cardboard
• An object at rest will remain at rest, and an object in motion will remain in motion, unless acted on by an unbalanced force
• Newton's second law of motion

  The acceleration of an object is directly proportional to the net force on it and inversely proportional to its mass
• Newton's law of acceleration

  Force acting on an object = Mass of object x Acceleration of object
• Greater mass of object


  Greater force needed to accelerate it
• Example of Newton's second law


  • Boy applies less force to accelerate bicycle than man due to less mass
  • Man applies more force to accelerate bicycle with added mass of woman
• Unit of force


  Newton (N = kg·m/s²)
• Weight


  Force due to gravity = Mass x Acceleration due to gravity (9.8 m/s²)
• Action and reaction forces

  Forces resulting from the interaction between two objects, where the size of the forces on the first object equals the size of the force on the second object, and the direction of the force on the first object is opposite to the direction of the force on the second object
• Newton's third law of motion (law of interaction)

  For every action, there is an equal and opposite reaction
• When a body exerts a force on another

  An equal amount of force is always exerted back on it
• Action-reaction force pairs


  • Make it possible for birds to fly
  • Make it possible for a ball to bounce
• Action-reaction force pairs


  • Girl sitting on a chair exerting a downward force, chair exerting an upward force
  • Bird's wings pushing air downwards, air pushing the bird upwards
  • Hand dribbling a ball with 3 newtons of force downwards, ground pushing the ball with 3 newtons of force
• Work


  Has many meanings, can refer to a job/employment, tasks/activities to accomplish, or an abstract idea related to energy
• Work


  • When work is done, it is accompanied by a change in energy
  • When work is done by an object, it loses energy
  • When work is done on an object, it gains energy
• Work is done


  1. Force is applied to an object

  2. Object moves in the direction of the force applied
• No work is done if the force exerted does not make the object move
• No work is done if the object moves in a direction that is not in the direction of the force applied
• Symbol for work


  Capital W
• Unit of work


  Newton meter (Joule)
• One Joule is the work done or energy expended in applying a force of one Newton through a distance of one meter
• Pushing a ball


  Work is done, transfers energy to the ball causing it to move continuously
• Work is done when the force applied to the object causes the object to have a displacement in the same direction as the force applied