IB Physics 2.2

Q: What is a force?

A: A force is an action that causes deformation or a change in velocity/acceleration of an object.

Q: What is the unit of force?

A: Newton (N)

Q: What is weight?

A: The attractive gravitational force exerted by an object’s mass on another object. Formula: W=mg

Q: What is electrostatic force?

A: The attractive or repulsive force between two charged objects.

Q: What is magnetic force?

A: The attractive or repulsive force between magnetic objects.

Q: What is reaction (normal) force?

A: The perpendicular force a surface exerts on an object due to its weight.

Q: What is friction?

A: The force parallel to a surface that opposes motion between two surfaces.

Q: What is compression?

A: The force exerted when an object (like a spring or rod) is squished. Acts inward on both sides.

Q: What is tension?

A: The force exerted when an object (like a rope or spring) is stretched. Acts outward on both sides.

Q: What does a free body diagram show?

A: All the forces acting on an object

Q: How is the magnitude of a force shown on a free body diagram?

A: By the length of the arrow — longer arrow = larger force.

Q: Where is weight drawn from on a free body diagram?

A: From the center of the object

Q: In a terminal velocity free body diagram, what two forces are equal?

Weight and Drag

Q: For a block moving at constant velocity, what two forces are equal?

• Applied Force = Friction

• Weight = Reaction (Normal)

Q: State Newton’s First Law.

A: A body remains at rest or moves at constant velocity unless acted upon by an external unbalanced force.

Q: What is equilibrium?

A: When all forces on an object balance out to zero.

Q: What are the two types of equilibrium?

A: Static: Object is stationary (e.g. Book on Table) B: Dynamic: Object moves at constant velocity 

Q: State Newton’s Second Law

A: The resultant force on an object is proportional to its acceleration. Formula: F=ma

Q: What is the difference between mass and weight?

A: Mass: Amount of matter (kg) Weight: Gravitational force on mass
W=mg

Q: State Newton’s Third Law.

A: When object A exerts a force on object B object B exerts an equal and opposite force on A. F of A on B = - F of B on A

Q: What is the key condition for Newton’s Third Law?

A: The forces must be of the same type (e.g. both contact forces or both gravitational)

Q: What is static friction?

A: The force that prevents motion between stationary surfaces.

Q: Formula for maximum static friction?

A:

Q: What is dynamic (kinetic) friction?

A: The frictional force acting on moving surfaces.

Q: Formula for maximum dynamic friction?

A:

Q: Relationship between static and dynamic friction?

A: Static is Greater than Dynamic

Q: What does “smooth surface” mean in IB questions?

A: The surface has no friction acting on the object.

Q: What type of forces act in a spring?

A: Compression and tension — both can occur depending on how it’s stretched or compressed.

Q: What is the spring constant (k)?

A: A measure of a spring’s stiffness

Q: Formula for elastic (spring) force?

A: F=kΔx

Q: Why does spring force not follow F = ma directly?

A: Because the force changes with extension — it’s not constant.