Newton's Laws (OCR GCSE Physics A (Gateway)): Flashcards

The equation for Newton's second law is F = mass × acceleration, where F is measured in Newtons.

False.

According to Newton's second law, acceleration is proportional to resultant force. If force doubles and mass stays the same, acceleration also doubles — not halves.

Using F = ma, rearranged to a = F ÷ m:

a = 20 ÷ 5 = 4 m/s²

The trolley accelerates at 4 m/s².

Complete the table using F = ma.

Inversely proportional means that as mass increases, acceleration decreases by the same factor, when the resultant force is kept constant.

Trolley C has the smallest acceleration. According to Newton's second law (a = F ÷ m), for the same force a greater mass produces a smaller acceleration — they are inversely proportional.

True.

From F = ma, if acceleration is kept constant, a larger mass requires a proportionally larger force. This is a direct consequence of Newton's second law.

For a given force, the greater the object's mass, the smaller the acceleration experienced.

The independent variable is the quantity deliberately changed by the experimenter. In Experiment 1 it is the force (F) — the mass of the trolley is kept constant.

True.

If masses are simply removed and set aside, the total mass of the system decreases, making it an unfair test. Transferring masses from the hanger to the trolley keeps total mass constant.

Pushing the trolley gives it an initial velocity not caused by the hanging force. Releasing it from rest ensures the only force accelerating it is the tension in the string from the hanging masses, making the results valid.

In Experiment 2, the mass on the trolley is changed while the force applied by the hanging masses remains constant.

The table below describes the two PAG experiments. Complete the missing cells.

A control variable is a quantity that is kept the same throughout an experiment so that it does not affect the dependent variable, ensuring a fair test.

True.

Random errors in timing — such as reaction time differences — vary unpredictably. Taking repeat readings and averaging them reduces the impact of these errors on the final result.

Do not stand directly beneath the mass hanger in case masses fall off the stack. A crash mat should be placed underneath to catch any falling masses.

Newton's third law states that whenever two bodies interact, the forces they exert on each other are equal in magnitude and opposite in direction.

A third law force pair always acts on different objects and the forces are always the same type.

False.

A Newton's third law pair must act on two different objects AND be the same type of force. Here, both forces act on the book — they are a Newton's first law example of balanced forces, not a third law pair.

The foot exerts a push force backward on the ground. The ground exerts an equal and opposite push force forward on the foot. Both forces are the same type (push/contact force) acting on different objects.

Complete the table identifying Newton's third law pairs for a book resting on a table.

A Newton's third law force pair consists of two forces that are equal in magnitude, opposite in direction, the same type, and act on two different interacting objects.

1. The two forces act on different objects

2. The forces are equal in size but act in opposite directions

3. The forces are the same type (e.g. both weight, both contact force)

True.

Newton's third law states that the forces are always equal in magnitude regardless of the masses involved. A small ball exerts the same force on the Earth as the Earth exerts on the ball — the difference in acceleration is due to the difference in mass.

Newton's third law is different from Newton's first law because it describes forces acting on different objects, whereas Newton's first law describes forces acting on a single object.

Inertia is the tendency of an object to continue in its state of rest, or in uniform motion, unless acted upon by an external force.

True.

A larger inertial mass means the object resists changes to its motion more strongly, so the same force produces a smaller acceleration.

Inertial mass is defined as the ratio between the force applied to an object and the acceleration it experiences.

Both use the same ratio: force divided by acceleration. Newton's second law (F = ma) is rearranged to m = F/a, which is the definition of inertial mass, so the two methods are equivalent.

Inertial mass is the property of an object that describes how difficult it is to change its velocity — defined as the ratio of force to acceleration (m = F/a).

True.

Inertia applies to both rest and motion. An object at rest will tend to remain at rest unless an external force acts on it — this resistance is inertia.

Complete the table to show how inertial mass affects acceleration when the same force is applied. (Higher Tier Only)

The object with the largest inertial mass will have the smallest acceleration. Since inertial mass = force/acceleration, and force is the same for all objects, mass is inversely proportional to acceleration.

Inertial mass is inversely proportional to acceleration for a given force — as inertial mass increases, acceleration decreases.

Momentum is a property of moving objects, calculated using the equation , where p is momentum (kg m/s), m is mass (kg) and v is velocity (m/s).

True.

Momentum = mass × velocity. If velocity = 0, then momentum = 0, regardless of the object's mass.

The unit of momentum is kilogram metre per second, kg m/s.

Momentum is a vector quantity, so its sign depends on direction. If one direction is defined as positive, an object moving in the opposite direction will have negative momentum.

The principle of conservation of momentum states that in a closed system, the total momentum before an event equals the total momentum after the event.

The rate of change of momentum is the force acting on an object — the larger the force, the greater and faster the change in momentum.

True.

Force equals the rate of change of momentum (F = Δp/Δt). For the same time interval, a larger force produces a larger change in momentum.

When a force acts on a moving object, it causes a change in momentum, and the force equals the rate of change of momentum.

Newton's second law gives F = ma. Acceleration is defined as the change in velocity divided by time, so F = m(Δv/Δt). Since momentum = mv, the change in momentum Δp = mΔv, which gives F = Δp/Δt.

Change in momentum (Δp) is the difference between final momentum and initial momentum: Δp = mv − mu, where v is final velocity and u is initial velocity.

False.

Both force and momentum are vector quantities — they have both magnitude and direction, so they can be positive or negative depending on the direction chosen.

Complete the table to show how changing one variable affects the force, given the equation F = Δp/Δt.

Force = change in momentum / time (F = Δp/Δt). If Δp is constant but the contact time increases, the force decreases — the same momentum change is spread over a longer time, reducing the peak force.