ForcesEdexcel GCSE Physics: Flashcards

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State Newton's first law.

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State Newton's first law.: If the resultant force on a body is zero it stays at rest or moves at constant velocity; if not zero, its speed and/or direction changes.
State Newton's second law as an equation.: F = m × a (force = mass × acceleration).
State the equation for weight.: W = m × g (weight = mass × gravitational field strength).
How is weight measured?: With a newtonmeter (calibrated spring balance) reading in newtons.
Define inertial mass.: A measure of how difficult it is to change an object's velocity, equal to force divided by acceleration.
Why does an object moving in a circle at constant speed have a changing velocity?: Because its direction is continuously changing, even though its speed stays the same.
What provides the centripetal force in circular motion, and in which direction does it act?: A resultant force acting towards the centre of the circle.
State Newton's third law.: When two objects interact, they exert equal and opposite forces on each other.
How does Newton's third law relate to collisions?: The equal and opposite forces act for the same time on each object, giving equal and opposite momentum changes, so total momentum is conserved.
In the Core Practical investigating force, mass and acceleration, what is varied?: The masses added to trolleys, while measuring the resulting acceleration.
What are the units of force, mass and acceleration in F = m × a?: Force in newtons (N), mass in kilograms (kg), acceleration in m/s².
Do a book's weight and the table's normal contact force on it form a Newton's third law pair?: No — they act on the same object (the book), so they are balanced forces, not a third law pair.
What two forces DO form a Newton's third law pair for a book on a table?: The book pushing down on the table, and the table pushing up on the book — equal, opposite, acting on different objects.
What happens to an object's motion if the resultant force on it is zero?: It continues at constant velocity (or stays at rest if already stationary).