Tug of war
Balanced and unbalanced forces.
Two teams, one rope
Two teams pull a rope in opposite directions. At first the rope does not move.
What do you think is true about the two pulls?
What this lesson covers
The idea
Two forces equal in magnitude but opposite in direction are balanced forces and cannot set an object at rest moving; unbalanced forces move it in the direction of the larger force.
Two teams, one rope
Two teams pull a rope in opposite directions. At first the rope does not move.
What do you think is true about the two pulls?
- They are equal in magnitude
- One is much bigger
- There is no pull at all
Pull the rope
Change the pull of each team.
Equal pulls, no motion
When both teams pulled equally, the rope stayed where it was. When one team pulled harder, the rope went its way. Forces that are equal and opposite are called balanced.
Two forces equal in magnitude but opposite in direction are balanced forces and cannot set an object at rest moving; unbalanced forces move it in the direction of the larger force.
Notes
Balanced forces (equal, opposite) cannot set a resting object moving. Unbalanced forces move it towards the larger force.
Check yourself
What are balanced forces?
Two teams pull a rope at rest with equal force in opposite directions. What happens?
Which pair of forces on a block is balanced?
One team pulls the rope harder. In which direction does the rope move?
- Two forces equal in magnitude but opposite in direction — correct. Yes!
- Two forces in the same direction. Forces in the same direction add up. Balanced forces are opposite in direction.
- Two forces of different strengths in opposite directions. These are unbalanced, because their magnitudes differ.
- The rope moves towards the left team. It would move that way only if the left team pulled with the larger force.
- The rope does not move — correct. Yes!
- The rope moves towards the right team. It would move that way only if the right team pulled with the larger force.
- 6 N to the right and 4 N to the left. These are opposite but not equal in magnitude, so they are unbalanced.
- 6 N to the right and 6 N to the right. These are equal but in the same direction, so they do not balance.
- 6 N to the right and 6 N to the left — correct. Yes!
- In the direction of the larger force — correct. Yes!
- In the direction of the smaller force. Unbalanced forces move the object in the direction of the larger force.
- It does not move. The rope does not move if the forces are balanced, but these forces are unbalanced.