Physics unit guide
Space, time and motion
Kinematics, forces, energy, momentum, circular motion and gravitation.
Unit 1 sets the habits that decide your grade in every later unit. Free-body diagrams and consistent sign conventions are not presentational - they are where the method marks live, and a student who draws forces before writing equations makes far fewer errors than one who does not. Momentum and energy questions in particular are usually solvable two ways, and choosing conservation over kinematics saves time on Paper 2.
Topics in this unit
What gets examined
- Selecting the right suvat equation from what is given and what is asked, without solving for intermediate quantities you do not need.
- Drawing free-body diagrams and resolving forces on an inclined plane.
- Applying conservation of momentum to collisions, and distinguishing elastic from inelastic.
- Work-energy problems where energy is transferred rather than conserved, including friction.
- Circular motion: recognising that centripetal force is provided by a real force, not added to the diagram.
- Newton's law of gravitation and orbital motion, including why orbital speed is independent of satellite mass.
How to revise it
Draw the free-body diagram first, always
Even for a question that looks like pure algebra. It earns marks on its own in longer questions and it prevents the sign errors that come from guessing a direction.
Declare positive before you start
Write "taking down as positive" at the top. Most momentum and kinematics errors are sign errors caused by an unstated convention that changed mid-question.
Reach for conservation before kinematics
If a question involves speeds at two points and no time, energy or momentum conservation is nearly always shorter than suvat, and shorter means fewer chances to slip.
Never draw centripetal force as an extra arrow
It is the resultant of forces already there - tension, gravity, normal. Adding it as a separate arrow is a conceptual error examiners specifically look for.
Where marks get lost
- Using suvat equations when acceleration is not constant.
- Forgetting that mass cancels in orbital and free-fall problems, then carrying it needlessly.
- Treating an inelastic collision as conserving kinetic energy - only momentum is conserved.
- Resolving weight along the wrong axis on an inclined plane.
- Giving a vector answer without a direction.
Practise this unit
Reading about a unit only goes so far. Work through real IB-style questions on it, with mark schemes.