Newton’s laws of motion Flashcards – AQA A-level Physics (7408)

What does Newton’s first law of motion state?

An object remains at rest or moves in a straight line at constant velocity unless a resultant external force acts on it.

What is an object’s acceleration when the resultant force on it is zero?

Zero.

What is inertia?

The tendency of an object to resist changes in its motion.

What is Newton’s second-law equation for an object of constant mass?

$\mathbf{F}_{\mathrm{net}} = m\mathbf{a}$

What is the direction of an object’s acceleration relative to the resultant external force?

The acceleration is in the same direction as the resultant force.

For a constant mass, how does acceleration magnitude change as the resultant force increases?

It increases.

For a given resultant force, how does acceleration magnitude change as mass increases?

It decreases.

What are the units of force, mass and acceleration?

• Force: newtons
• Mass: kilograms
• Acceleration: metres per second squared

What does Newton’s third law say about the forces between two interacting objects?

Each object exerts a force on the other simultaneously; the forces have equal magnitude and opposite directions.

Why do Newton’s third-law force pairs not cancel as forces on a single object?

The two forces act on different objects.

What does a free-body diagram represent?

One chosen object in isolation, with the external forces acting on it shown as labelled arrows.

What do the direction and length of a force arrow represent in a free-body diagram?

The arrow’s direction shows the force direction. Its length can represent the force magnitude when a scale is used.

How can a free-body diagram support analysis of an object's motion?

The forces on the object can be combined to determine the resultant force.

Is a force exerted by the chosen object on another object drawn on the chosen object's free-body diagram?

No. It is not a force acting on the chosen object.