5 IB Physics Traps You Keep Falling For (And How to Dodge Them)

5 IB Physics Traps You Keep Falling For (And How to Dodge Them)
Let’s be real for a second: IB Physics is incredibly tricky. You can memorize every single formula in the data booklet and still drop marks on the exam because the core concepts are hiding a few logical traps.

If you have ever gotten a question wrong and thought, "Wait, but that makes no sense!" you are not alone. Examiners love to test your true understanding of physics by setting up questions that prey on common intuitive mistakes.

The good news? Once you know what these traps look like, you will never fall for them again. Here are the five most common misconceptions in the IB Physics syllabus, and the reality checks you need to fix them before exam day.

 
Misconception 1: "Zero velocity means zero acceleration."
The Myth: If an object is momentarily stopped, it cannot possibly be accelerating.

The Reality: Acceleration is the rate of change of velocity, not the velocity itself. The absolute classic IB trap for this is throwing a ball straight up into the air.

At the exact peak of its flight, the ball stops moving for a split second, meaning its velocity is $v = 0$. However, gravity has not magically turned off. The Earth is still pulling on the ball, which means the acceleration is $a = 9.81\text{ m s}^{-2}$ downwards. If the acceleration were truly zero at the peak, the ball would just float there in mid-air forever!

Misconception 2: "Normal force and gravity are a Newton's Third Law pair."
The Myth: When a book rests on a table, gravity pulls it down and the normal force pushes it up. Because these forces are equal and opposite, they must be a Newton's Third Law pair.

The Reality: This is a Newton's First Law equilibrium pair, not a Third Law pair!

For two forces to be a Newton's Third Law pair, they must act on two different objects (Object A pushes Object B, so Object B pushes Object A). In the case of the book, both gravity and the normal force are acting on the same object (the book).

The true Third Law pair for gravity (the Earth pulling down on the book) is the book pulling up on the Earth with an equal gravitational force.
The true Third Law pair for the normal force (the table pushing up on the book) is the book pushing down on the table.
Misconception 3: "Current gets 'used up' as it goes through a circuit."
The Myth: As electrons flow through a resistor or a lightbulb, the component "consumes" the current, meaning there is less current flowing out of the resistor than flowing into it.

The Reality: Current is the rate of flow of charge, and charge is strictly conserved (Kirchhoff’s First Law). Every single electron that enters a resistor must exit the other side.

What actually gets "used up" or transferred is energy. Electrons enter the resistor with high electrical potential energy and leave with lower potential energy, having transferred that energy into heat or light. We measure this drop in energy per unit charge as potential difference (voltage). So, current stays constant in a series circuit; it is the voltage that drops!

Misconception 4: "Heat and temperature are the same thing."
The Myth: A cup of boiling water contains a lot of "heat," and its temperature is just a measurement of that heat.

The Reality: In physics, these are two entirely different concepts that cannot be used interchangeably.

Temperature is a scalar measurement of the average random kinetic energy of the particles in a substance.
Heat is the transfer of thermal energy between two systems due to a temperature difference.
An object cannot "contain" heat. It contains internal energy. Heat is just the verb—it is the energy in transit from a hotter object to a colder one.

Misconception 5: "Particles travel along with the wave."
The Myth: When you watch a wave roll across the surface of the ocean, the water molecules are traveling across the ocean along with the wave.

The Reality: Mechanical waves transfer energy, not matter.

If you place a rubber duck on the surface of the water, as the wave passes, the duck (and the water molecules beneath it) will only oscillate up and down around a fixed equilibrium position. The particles bump into their neighbors, passing the energy along, but they themselves stay roughly in the exact same spot. It is the disturbance that travels, not the medium itself.