02.2 - Forces

Topic Subpages:

02.2 Forces
- Balanced Forces Model
- Unbalanced Forces Model
  - Unbalanced Forces Practica
  - Unbalanced Forces Problem Solving

02.1 - Kinematics

Constant Velocity

Uniform Acceleration

02.2 - Forces

Balanced Forces Model

Unbalanced Forces Model

2D Motion

02.3 - Work, Energy, Power

02.4 - Momentum and Impulse

Essential idea: Classical physics requires a force to change a state of motion, as suggested by Newton in his laws of motion.

Using mathematics: Isaac Newton provided the basis for much of our understanding of forces and motion by formalizing the previous work of scientists through the application of mathematics by inventing calculus to assist with this. (2.4)

Intuition: The tale of the falling apple describes simply one of the many flashes of intuition that went into the publication of Philosophiæ Naturalis Principia Mathematica in 1687. (1.5)

Understandings:

Objects as point particles
Free-body diagrams
Translational equilibrium
Newton’s laws of motion
Solid friction

Applications and skills:

Representing forces as vectors
Sketching and interpreting free-body diagrams
Describing the consequences of Newton’s first law for translational equilibrium
Using Newton’s second law quantitatively and qualitatively
Identifying force pairs in the context of Newton’s third law
Solving problems involving forces and determining resultant force
Describing solid friction (static and dynamic) by coefficients of friction

Guidance:

Students should label forces using commonly accepted names or symbols (for example: weight or force of gravity or mg)
Free-body diagrams should show scaled vector lengths acting from the point of application
Examples and questions will be limited to constant mass
mg should be identified as weight
Calculations relating to the determination of resultant forces will be restricted to one- and two-dimensional situations

Data booklet reference:

F=ma
F_f≤μ_sR - or - F_f≤μ_sN
F_f=μ_dR - or - F_f=μ_dN

Theory of knowledge:

Classical physics believed that the whole of the future of the universe could be predicted from knowledge of the present state. To what extent can knowledge of the present give us knowledge of the future?

Utilization:

Motion of charged particles in fields (see Physics sub-topics 5.4, 6.1, 11.1, 12.2)
Application of friction in circular motion (see Physics sub-topic 6.1)
Construction (considering ancient and modern approaches to safety, longevity and consideration of local weather and geological influences)
Biomechanics (see Sports, exercise and health science SL sub-topic 4.3)

Aims:

Aims 2 and 3: Newton’s work is often described by the quote from a letter he wrote to his rival, Robert Hooke, 11 years before the publication of Philosophiæ Naturalis Principia Mathematica, which states: “What Descartes did was a good step. You have added much several ways, and especially in taking the colours of thin plates into philosophical consideration. If I have seen a little further it is by standing on the shoulders of Giants.” It should be remembered that this quote is also inspired, this time by writers who had been using versions of it for at least 500 years before Newton’s time
Aim 6: experiments could include (but are not limited to): verification of Newton’s second law; investigating forces in equilibrium; determination of the effects of friction