What is a force?
An interaction that can change an object’s velocity (speed and/or direction) or shape.
State Newton’s First Law.
An object remains at rest or in uniform motion unless a net force acts on it.
What does Newton’s First Law imply about forces?
Net force = 0 → constant velocity
Net force ≠ 0 → velocity changes
What does it mean if forces are balanced?
Resultant force = 0, so no acceleration.
What does it mean if forces are unbalanced?
Resultant force ≠ 0, so the object accelerates.
State Newton’s Second Law.
The acceleration of an object is directly proportional to the net force, in the same direction, and inversely proportional to its mass.
Write Newton’s Second Law as an equation.
F=ma
Where:
𝐹
F = resultant force
𝑚
m = mass
𝑎
a = acceleration
What determines the direction of acceleration?
The direction of the resultant force.
What is mass?
A measure of an object’s resistance to acceleration (inertia).
What is weight?
The force acting on a mass due to gravity.
State the equation linking weight and mass.
W=mg
What is a free body diagram?
A diagram showing all forces acting on an object, represented by arrows.
What must be included in a correct FBD?
Only forces acting on the object
Arrows showing direction
Correct force labels
What is the normal contact force?
The force exerted by a surface perpendicular to the surface.
Why do objects accelerate down an inclined plane?
Because a component of weight acts parallel to the surface, producing a net force.
Because a component of weight acts parallel to the surface, producing a net force.
Component parallel to slope causes acceleration
Component perpendicular is balanced by the normal force
How is Newton’s Second Law used in calculations?
Draw a free body diagram
Resolve forces if necessary
Find the resultant force
Apply F=ma
: What mistakes commonly lose marks in dynamics questions?
Forgetting forces are vectors
Missing forces on FBDs
Using velocity instead of acceleration in Newton’s laws
Incorrect direction for resultant force
Which is the correct statement of Newton’s Second Law?
The acceleration of an object produced by a net force is directly proportional to the force, in the same direction, and inversely proportional to the mass.
