GCSE Physics revision

Newton's First Law

Forces, accelerations and Newton's Laws of motion

AQA 4.5.6.2.1

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AQA student objectives

Learning pathway

ALL 🎯

Apply Newton’s First Law to explain the motion of objects moving with a uniform velocity and objects where the speed and/or direction changes.

MOST 🎯🎯

Interpret results or representations related to newton's first law.

SOME 🎯🎯🎯

Analyse an unfamiliar problem involving newton's first law and justify the method or conclusion.

Revision summary

Read on screen, then print for Cornell-style active revision.

Newton's first law states that a resultant force is required to change the motion of an object — without one, motion stays the same.
A stationary object with zero resultant force will remain stationary, and a moving object with zero resultant force will continue at the same velocity.
This law applies to both stationary and moving objects, meaning balanced forces always result in unchanged motion.

1. Newton's First Law of MotionAQA

Newton's first law states that a resultant force is required to change the motion of an object — without one, motion stays the same.
A stationary object with zero resultant force will remain stationary, and a moving object with zero resultant force will continue at the same velocity.
This law applies to both stationary and moving objects, meaning balanced forces always result in unchanged motion.

A resultant force is the single overall force that results from combining all forces acting on an object.
If force arrows are unequal in opposite directions, there is a non-zero resultant force, causing the object to accelerate in the direction of the larger force.
A non-zero resultant force means the forces are unbalanced, which is the condition required for acceleration to occur.

2. Resultant Force and Unbalanced ForcesAQA

A resultant force is the single overall force that results from combining all forces acting on an object.
If force arrows are unequal in opposite directions, there is a non-zero resultant force, causing the object to accelerate in the direction of the larger force.
A non-zero resultant force means the forces are unbalanced, which is the condition required for acceleration to occur.

Newton's second law states that a non-zero resultant force acting on an object will cause it to accelerate.
The resultant force is directly proportional to the acceleration it produces — doubling the force doubles the acceleration.
The relationship is expressed as F = ma, where F is resultant force in newtons (N), m is mass in kilograms (kg), and a is acceleration in m/s².

3. Newton's Second Law of MotionAQA

Newton's second law states that a non-zero resultant force acting on an object will cause it to accelerate.
The resultant force is directly proportional to the acceleration it produces — doubling the force doubles the acceleration.
The relationship is expressed as F = ma, where F is resultant force in newtons (N), m is mass in kilograms (kg), and a is acceleration in m/s².

If a stationary object experiences a resultant force, it will begin to move in the direction of that force.
If an object is already moving in the same direction as the resultant force, it will speed up.
If the resultant force acts opposite to the direction of motion, the object will slow down or potentially stop entirely.
A resultant force can also cause a change in direction without a change in speed, which still counts as acceleration.

4. Five Possible Effects of AccelerationAQA

If a stationary object experiences a resultant force, it will begin to move in the direction of that force.
If an object is already moving in the same direction as the resultant force, it will speed up.
If the resultant force acts opposite to the direction of motion, the object will slow down or potentially stop entirely.
A resultant force can also cause a change in direction without a change in speed, which still counts as acceleration.

Acceleration is defined as the change in velocity divided by the change in time: a = Δv
Δt
.
Velocity is a vector quantity determined by both speed and direction, so a change in direction alone constitutes a change in velocity.
The Moon orbits the Earth at a constant speed but is always accelerating because its direction continuously changes.
The Earth's gravitational pull acts perpendicular to the Moon's motion, keeping it in a circular orbit with a constantly changing velocity.

5. Circular Motion and Changing VelocityAQA

Acceleration is defined as the change in velocity divided by the change in time: a = Δv
Δt
.
Velocity is a vector quantity determined by both speed and direction, so a change in direction alone constitutes a change in velocity.
The Moon orbits the Earth at a constant speed but is always accelerating because its direction continuously changes.
The Earth's gravitational pull acts perpendicular to the Moon's motion, keeping it in a circular orbit with a constantly changing velocity.

To find acceleration, first calculate the resultant force by subtracting the smaller force from the larger: e.g. 42 N − 30 N = 12 N to the right.
Rearranging F = ma gives a = m F
, so with a mass of 0.25 kg and a resultant force of 12 2
12 N, the acceleration is 0.25
= 48 m/s .

Inertia is the tendency of an object to resist changes to its motion — objects at rest stay at rest and objects in motion stay in motion unless acted on by a resultant force.
Inertial mass measures how difficult it is to change an object's velocity, and is found using m = Fa from Newton's second law.
A larger inertial mass means a greater force is needed to produce the same acceleration, so massive objects like the Moon are very hard to accelerate.

7. Inertia and Inertial MassAQA

Inertia is the tendency of an object to resist changes to its motion — objects at rest stay at rest and objects in motion stay in motion unless acted on by a resultant force.
Inertial mass measures how difficult it is to change an object's velocity, and is found using m = Fa from Newton's second law.
A larger inertial mass means a greater force is needed to produce the same acceleration, so massive objects like the Moon are very hard to accelerate.