Balanced forces
In a tug of war, both teams pull on the rope with all their strength and yet the rope does not move. Does that mean there are no forces acting? Quite the opposite: there are two enormous forces, but they cancel each other out.
The net force: adding forces in the same direction
Two classmates push a table towards the door at the same time and find that it moves much faster than when only one of them pushes it, but if they push from opposite sides, facing each other, the table barely moves: how are several forces combined to produce a single effect on a body?
Jorge pushes a box to the right with $3\ \text{N}$ and Elena also pushes it to the right with $4\ \text{N}$, as shown in the figure. a) Calculate the net force on the…
Jorge pushes a box to the right with $3\ \text{N}$ and Elena also pushes it to the right with $4\ \text{N}$, as shown in the figure.
- a) Calculate the net force on the box.
- b) In which direction will the box move?
Two children push a table in opposite directions: one exerts $10\ \text{N}$ to the right and the other, $6\ \text{N}$ to the left, as shown in the figure. a) What is the…
Two children push a table in opposite directions: one exerts $10\ \text{N}$ to the right and the other, $6\ \text{N}$ to the left, as shown in the figure.
- a) What is the value of the net force on the table?
- b) Which way does the table move?
Three forces act on a box along the same line: $2\ \text{N}$ and $3\ \text{N}$ to the right, and $5\ \text{N}$ to the left. a) Calculate the net force on the box. b)…
Three forces act on a box along the same line: $2\ \text{N}$ and $3\ \text{N}$ to the right, and $5\ \text{N}$ to the left.
- a) Calculate the net force on the box.
- b) Will the box move? Justify your answer.
Equilibrium: when the net force is zero
A lamp hangs from the ceiling without moving, as shown in the figure. a) Name the two forces acting on it and state which direction each one points in. b) Is the lamp in…
A lamp hangs from the ceiling without moving, as shown in the figure.
- a) Name the two forces acting on it and state which direction each one points in.
- b) Is the lamp in equilibrium? Justify your answer.
A book is resting on a table, as shown in the figure. Are any forces acting on it? State the forces present and explain why the book does not move.
A book is resting on a table, as shown in the figure.
Are any forces acting on it? State the forces present and explain why the book does not move.
A drone hovers stationary in the air, neither rising nor falling. Its weight is $50\ \text{N}$, as shown in the figure. a) What is the upward force exerted by its…
A drone hovers stationary in the air, neither rising nor falling. Its weight is $50\ \text{N}$, as shown in the figure.
- a) What is the upward force exerted by its propellers?
- b) To start ascending, must this force be greater than, less than, or equal to the weight? Justify your answer.
Adding forces that are not in the same direction
When two forces do not point along the same line, it is not enough to add or subtract the numbers: they have to be added as arrows (vectors), taking their direction into account.
In the tug-of-war final, three students participate per team. The red team pulls to the left with forces of $150\ \text{N}$, $140\ \text{N}$, and $160\ \text{N}$; the…
In the tug-of-war final, three students participate per team. The red team pulls to the left with forces of $150\ \text{N}$, $140\ \text{N}$, and $160\ \text{N}$; the blue team pulls to the right with $145\ \text{N}$, $155\ \text{N}$, and $140\ \text{N}$.
- a) Calculate the total force of each team.
- b) What is the value of the net force and in which direction does it point?
- c) What additional force does the losing team need to balance the rope?
Read this statement: "If the net force on an object is zero, no forces are acting on it." a) Think of a rucksack hanging from a coat peg and explain why the statement is…
Read this statement: "If the net force on an object is zero, no forces are acting on it."
- a) Think of a rucksack hanging from a coat peg and explain why the statement is false.
- b) Write down the corrected statement.
- c) Give another everyday example of an object in equilibrium on which at least two forces are acting.