🪢 Resultant Force: Tug of War

Hello! Pandi and Pengu are playing tug of war. Which way will the rope go? We will find out by adding and subtracting forces.

We show a force with an arrow. The arrow points in the direction of the force. The length of the arrow shows how big the force is: the 40 N arrow is twice as long as the 20 N arrow. The unit of force is the newton (N).

Mina pushes the crate with 30 N. Sam pulls on the rope with 20 N. Both go to the right. Let’s put the arrows end to end: the forces add up. The total force on the crate is called the resultant force: 30 + 20 = 50 N, to the right.

Now for tug of war! The blue team has two players: 30 N and 20 N, 50 N to the left in total. The orange team pulls to the right with 30 N. In opposite directions we subtract the smaller from the bigger: 50 − 30 = 20 N. The resultant force points left, and the flag slides left.

This time both teams pull with 40 N. The forces are equal and opposite: 40 − 40 = 0 N. The resultant force is zero, and the flag stays where it is. We call these balanced forces.

Balanced forces do not change how something is moving. A crate that is still stays still, even when it is pushed from both sides with 5 N. A moving cart, with 10 N forwards and 10 N backwards, keeps going in the same direction at the same speed.

The cart goes 2 metres every second: 2 m in 1 second, 4 m in 2 seconds, 6 m in 3 seconds. If it covers equal distances in equal times, the motion has a steady speed.

To find the speed, we divide the distance travelled by the time taken: speed = distance ÷ time. The cart went 6 metres in 3 seconds: 6 ÷ 3 = 2 m/s. Speed tells us how many metres we travel every second.

Does the team with more players always win? No! The blue team has 3 players, each pulling with 10 N: 30 N in total. The orange team has 2 players, each pulling with 20 N: 40 N in total. The resultant is 40 − 30 = 10 N, to the right. What matters is not the number of players but the total force.

Summary: forces in the same direction add up, forces in opposite directions subtract. When equal and opposite forces give a resultant of 0 N, the forces are balanced and the motion does not change. Speed is distance divided by time. Now try it in Sky Laboratory!