P10 - forces and motion

• Newtons first Law explained

  • If the resultant force on a stationary object is 0 it will remain stationary
  • If the resultant force is 0 on an moving object it will continue moving at The same velocity
• What happens to a stationary object with no resultant forces?


  It remains stationary
• What will happen to a stationary Object with a resultant force on it( unbalanced force) 


  Accelerate in the direction of the force
• What happens to a moving object with no resultant force on it(balanced forces)

  It will remain at the same velocity
• What happens when a moving object has a resultant force on it in the direction it’s moving

  It will accelerate in the direction of the force
• What happens to a moving object when there’s a resultant force on it( unbalanced force) in the opposite direction

  The speed will decrease and accelerate in the direction of the force
• What is the relationship described in Newton's Second Law of Motion?

  • Acceleration (a) ∝ Resultant Force (F)
  • Acceleration (a) ∝ 1/Mass (m)
  • Combined: \( a \propto \frac{F}{m} \)
• Newton’s second law explained

  The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the mass of the object
• Newton second law equation

  Force = mass x acceleration
• Inertial mass definition 


  It is a measure of how difficult it is to change the velocity of an object
• Mass definition

  How much matter an object has in it
• Weight definition 


  The force acting on it due to gravity
• Weight of an object equation

  Weight = mass x gravitational field strength
• Centre of mass definition

  The weight of an object can be considered to act as a single point
• Equation for force spring constant and extension 


  Force = spring constant x extension
• Inelastic deformation 


  Doesn’t go back to original shape when forces are removed
• Elastic deformation 


  When the forces are removed it goes back to original shape
• Stopping distance definition 


  the distance the car travels after the driver has spotted a hazard
• Thinking distance definition 


  The distance the vehicle travels During the reaction time
• Braking distance 


  The distance the vehicle travels after the brakes have been applied
• How to calculate stopping distance?

  Thinking distance + braking distance
• Thinking distance factors

  • Drugs
  • Distractions
  • Alcohol
  • Tiredness
• Braking distance factors

  • Wet icy conditions
  • Worn brakes
  • Worm tyres
• kinetic energy equation 


  Kinetic energy = 0.5 x mass x velocity x velocity
• Momentum units 


  Kgm/s
• Momentum equation 


  Momentum = mass x velocity
• Conservation of momentum 


  In a closed system the total momentum before is equal to the total momentum after an event
• Terminal velocity 


  When the drag on a falling object becomes equal to the gravitational force accelerating it downwards the resultant force becomes 0 and moves at a constant speed
• If the velocity of an object changes it must be acted on by a resultant force.

  The acceleraction in the same direction as the resultant force.
• Equation that links distance speed and time


  Distance = speed x time
• Why can an object travelling at a constant speed in a circle not have constant velocity?

  • Velocity is a vector quantity and this means it can only be constant if the direction is constant.
  • In a circular motion the direction is continuously changing
• Newton’s third law


  Whenever two objects interact the forces they exert on each other are always equal and opposite.