Force

• • A force is a pull or a push of one thing on another.
  • It is a vector quantity.
  • Its S.I unit is newtons (N)
• The effects of force are:

  • It can speed up or slow down moving objects.
  • It can change the shape of an object.
  • It can change the direction of a moving object.
  • It can make a stationary object move.
• The seven types of forces are:

  1. Gravitational force
  2. Normal reaction force
  3. Air resistance force
  4. Upthrust force
  5. Magnetic force
  6. Electrostaitc force
  7. Nuclear force
• • Gravitational force is the force on a body due to the pull of gravity.
  • It is also called weight and weight can be calculated by using this formula.$Weight=$$m x g$
• • Normal reaction force is the upward force on a body from the surface it is resting on.
  • The normal reaction force prevents the object from sitting into the surface it is resting on.
• • Air resistance is a force that opposes movement of objects through air.
  • Drag is a force that opposes motion of objects through fluids.
• • Upthrust force is an upward force on an object immersed in a fluid.
  • It is done to the difference in pressure at the top and at the bottom of the object.
• Magnetic force is the force experienced when two magnets are brought close to each other.
• Electrostatic force are the forces between charges. Like charges repel while unlike charges attract.
• Nuclear force is the force holding the nucleus of an atom together.
• • Balanced forces are forces of the same size but act in the opposite directions in the same line of action.
  • Balanced forces are also said to be in equilibrium (meaning they are in balance).
• Unbalanced forces are forces that will make an object to accelerate in the direction of the force.
• Springs and wires will stretch when a force is attached on them. They will return to their original length when the force is removed so long as they are not stretched beyond a certain limit.
• • Hooke's Law states that extension is directly proportional to force provided the elastic limit is not exceded.
• Elastic bands don't obey Hooke's Law when force is applied to them.
• Friction is the force that opposes the motion of two objects sliding over each other.
• • Safe stopping distance is the thinking distance and braking distance.
  • Thinking distance is the distance travelled by a car before applying the brakes after seeing an obstacle.
  • Reaction time is the time taken before the driver applies the brakes after he has seen an obstacle.
  • Braking distance is the distance travelled by a vehicle after the brakes have been applied.
• Momentum is a quantity possessed by an object in motion.

  It's S.I unit is Kgm/s and it's a vector quantity.

  $momentum=$$mass x velocity$
• The principle of momentum states that: The total momentum before collision is equal to the total momentum after collision provided no external forces act on the objects.
• • Elastic collision is a collision in which momentum and kinetic energy of the colliding objects is conserved.
  • Inelastic collision is a collision in which momentum is conserved but K.E is not conserved.
• • Newton's First law states that: A body will continue with it's state of rest or uniform motion unless acted on by another force.
  • Newton's Second law states that: The rate of change of momentum is directly proportional to the force applied.
  • Newton's Third law states that: If body A applies a force on body B, body B will also apply an equal and opposite force on body A.
• Moment is the turning effect of a force.

  $Moment=$$F X d$
• Principle of moments states that: At equilibrium the sum of clockwise moments is equal to the sum of anticlockwise moments.