What Is a Force? - ScienceKid.org

Forces are all around you — pushing, pulling, stretching, and squeezing. Learn what scientists mean by a force, how we measure and represent forces, and why understanding them is the key to understanding all motion.

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5–10 min

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Q1 Question 1 of 10

What is a force?

The speed at which an object is moving A push or a pull that acts on an object The energy stored inside an object The weight of an object measured in kilograms

Q2 Question 2 of 10

What is the SI unit used to measure force?

Joule (J) Kilogram (kg) Newton (N) Watt (W)

Q3 Question 3 of 10

Which of these is a contact force?

Gravity pulling the Moon towards Earth Friction between a sliding book and a table Magnetism attracting a nail to a magnet without touching The electrostatic force holding a balloon to a wall after rubbing

Q4 Question 4 of 10

Which of these is a non-contact force?

Air resistance slowing a cyclist down A hand pushing a shopping trolley Tension in a rope holding a swing Gravity pulling a skydiver towards Earth

Q5 Question 5 of 10

You kick a football. Your foot is in contact with the ball for only a fraction of a second, yet the ball flies through the air. What force keeps the ball moving after your foot leaves it?

A forward force from the kick that stays in the ball Air pressure pushing it from behind No force is needed to keep it moving — it continues because of its inertia Gravity acts forward on the ball through the air

Q6 Question 6 of 10

A free-body diagram is used to show forces on an object. What does each arrow in a free-body diagram represent?

The speed of the object in a particular direction A single force — its direction shows where the force acts and its length shows the force's size The path the object will take through space The energy stored in the object at that moment

Q7 Question 7 of 10

A book rests on a table. Two forces act on it: gravity pulls it down and the table pushes it up. These two forces are equal in size and opposite in direction. What do we say about the forces?

The forces are unbalanced The forces are balanced Only one force acts because the table cancels out gravity The net force is downward because gravity is always stronger

Q8 Question 8 of 10

What is the 'normal force'?

The average of all forces acting on an object The force of gravity on any surface The contact force a surface exerts on an object perpendicular to the surface The frictional force acting parallel to a surface

Q9 Question 9 of 10

Which of the following would cause the forces on a stationary car to become unbalanced?

Gravity increases because the engine is running The normal force from the road suddenly disappears The engine applies a forward driving force greater than the friction and air resistance Air resistance doubles when the engine is switched on

Q10 Question 10 of 10

A tug-of-war team pulls a rope to the right with 500 N and another team pulls to the left with 500 N. What is the net force on the rope?

1000 N — you add the forces together 500 N to the right — the first team's force wins 0 N — the forces are balanced and there is no net force 250 N to the left — you average the two forces

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