Question

1. if an object is not moving, and all the forces acting on it are equal and opposite, the object is in a state of ______.
2. when you push a box across the floor, the force you use is called an ______ force.

word bank: gravity applied friction equilibrium rest
multiple choice questions: circle the letter of the correct answer from the choices for each question.

1. which of the following describes a situation in equilibrium?

a) a car speeding up
b) a ball rolling to a stop
c) a book resting on a table
d) a person jumping

1. what is the net force on an object in equilibrium?

a) greater than zero
b) equal to the weight of the object
c) zero
d) equal to gravity

1. which force must be overcome to start moving an object that is at rest? a) gravity b) air resistance c) friction d) applied
2. if you hang a picture on the wall and it does not move, which statement is true?

a) the forces are unbalanced
b) the net force is zero
c) gravity is not acting on the picture
d) there are no forces acting

Explanation:

• Question 1:
• An object in equilibrium has no net force acting on it and is either at rest or moving at a constant velocity.
• A car speeding up (a) has a net force (accelerating), a ball rolling to a stop (b) has a net force (decelerating due to friction), a person jumping (d) has a net force (pushing off the ground).
• A book resting on a table (c) has equal and opposite forces (gravity down, normal force up), so it is in equilibrium.
• Question 2:
• By definition, in equilibrium, the net force (\(F_{net}=\sum F\)) is zero.
• Question 3:
• Friction is the force that opposes the relative motion between two surfaces in contact. When an object is at rest, static friction must be overcome to start moving it.
• Question 4:
• If the picture does not move, it is in equilibrium.
• In equilibrium, the net force is zero (\(F_{net} = 0\)). Gravity is acting on the picture (pulling it down), and there is a tension force (from the hanging mechanism) pulling it up (balanced forces).

Answer:

1. C. A book resting on a table
2. C. Zero
3. C. Friction
4. B. The net force is zero