Direction of a normal reaction?

Perpendicular to the surface, away from it.

The pulling force in a string, rope or cable, acting along it.

Thrust or compression?

The pushing force along a rod or strut.

Name two resistance forces.

Friction and air resistance, both opposing motion.

A car moves at constant speed. How does the driving force compare with the resistance?

They are equal in size and opposite in direction.

What condition applies to forces on a particle moving at constant velocity?

They sum to the zero vector: \mathbf{0}.

Is a force needed to keep a body moving at constant velocity?

No. A resultant force is needed only to change the velocity.

What does 'light' mean for a string?

The string has negligible mass.

Forces and Newton's first lawEdexcel A-Level Maths: Flashcards

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State Newton's first law.

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State Newton's first law.: A body remains at rest or moves with constant velocity unless a resultant force acts on it.
What is the resultant force on a body moving at constant velocity?: Zero.
What is the unit of force?: The newton (N).
Direction of a normal reaction?: Perpendicular to the surface, away from it.
What is tension?: The pulling force in a string, rope or cable, acting along it.
Thrust or compression?: The pushing force along a rod or strut.
Name two resistance forces.: Friction and air resistance, both opposing motion.
How is weight directed?: Vertically downwards.
A car moves at constant speed. How does the driving force compare with the resistance?: They are equal in size and opposite in direction.
How do you find the magnitude of $(a\mathbf{i}+b\mathbf{j})$ N?: $\sqrt{a^2+b^2}$
What condition applies to forces on a particle moving at constant velocity?: They sum to the zero vector: $\mathbf{0}$ .
Is a force needed to keep a body moving at constant velocity?: No. A resultant force is needed only to change the velocity.
What does 'light' mean for a string?: The string has negligible mass.

Exam questions on Forces and Newton's first law

A box of weight $200$ N rests on a rough horizontal floor. A horizontal force of $35$ N pushes on the box, but the box does not move. Model the box as a particle.
The push is increased to $60$ N and the box now moves along the floor at a constant speed. State the magnitude of the resistance to the box's motion and justify your answer.2 marks
A car travels along a straight horizontal road at a constant speed of $25$ m s $^{-1}$ . The engine provides a driving force of $1800$ N. Model the car as a particle.
Explain why the engine must provide a driving force even though the car is moving at constant speed.2 marks
Three horizontal forces act on a particle: $\mathbf{F}_1=(3\mathbf{i}+5\mathbf{j})$ N, $\mathbf{F}_2=(-7\mathbf{i}+2\mathbf{j})$ N and $\mathbf{F}_3=(p\mathbf{i}+q\mathbf{j})$ N, where $\mathbf{i}$ and $\mathbf{j}$ are perpendicular unit vectors. The particle moves with constant velocity.
Find the values of $p$ and $q$ .3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).