Forces, Motion, & Energy - Notes

Year 10 Physics: Forces, Motion, & Energy

Area of Study 1: Forces, Motion, & Energy - Lesson 5

  • Objectives:
    • Analyze graphically, numerically, and algebraically, straight-line motion under constant acceleration.
    • Apply the vector model of forces, including vector addition and components of forces.

Goal

  • Apply Newton’s First Law of Motion both theoretically and mathematically.
Success Criteria
  • I can:
    • Describe Newton’s First Law of Motion.
    • Calculate the net force acting on an object.
    • Determine the effect of the net force on an object with reference to Newton’s first law.
  • Question: Why do objects change their speed?

Key Vocabulary

  • Accelerate
  • Net Force
  • Inertia

Why Do Objects Change Their Speed?

  • This question is central to understanding forces and motion.

Newton’s First Law

  • Newton's First Law: Every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external, net force.
  • Inertia: The tendency to resist changes in a state of motion.

Net Force

  • Definition: The sum of all the forces acting on an object.
  • Nature: Vector quantity (has both magnitude and direction).
  • Formula: Fnet=∑FF_{net} = \sum F
  • If two forces act in opposite directions, the net force is the difference between the greater and smaller force.
  • The object will accelerate in the direction of the net force.
Balanced Forces
  • Do not cause a change in motion (Newton’s First Law).
  • Opposite in direction.
  • Equal in magnitude.
Unbalanced Forces
  • Occur when one force is greater in magnitude than the other.
  • Shows the effect of force on the object - causes the object to accelerate.
  • Can be in the same or opposite direction.

Free Body Diagrams

  • Physicists use free body diagrams to represent complex objects with detail.

Representing Force

  • Force is a vector quantity.
  • Represented with an arrow:
    • The length of the arrow indicates the magnitude of the force.
    • The arrowhead shows the direction.

Application Questions (Net Force Examples)

  • Examples with multiple forces acting on objects, requiring calculation of net force.

Changing Speed in a Car

  • Illustrates real-world applications of forces and motion.

Braking Distance

  • Braking distance depends on how fast a vehicle is traveling before the brakes are applied, and is proportional to the square of the initial speed.
  • Even small increases in speed mean significantly longer braking distances.
  • Wipe Off 5 Road Safety Campaign
    • Reduce speeding.
    • Educate road users about the dangers of traveling, even a little, over the speed limit.
    • Reducing average speed by 5 km/h could save lives and prevent serious injuries.

Review Questions

  • What happens to the moose if you’re driving while on your phone?
  • What happens to the moose if you’re travelling at a higher speed?
  • Why do speed limits exist? Why are they different? (e.g., school zones vs. highways)