Weight
This quantity is measured in kilograms and does not change when you travel to the Moon.
What is mass?
This force opposes motion or attempted motion between surfaces.
What is friction?
A free body diagram should show all the ______ acting on an object.
What are forces?
A car moves east at constant speed. What is the net force acting on the car?
What is zero newtons?
An object has a mass of 10 kg. Calculate its weight on Earth.
98 N
An astronaut's mass remains constant on the Moon, but this quantity changes.
What is weight?
Cleats on a soccer shoe increase this quantity between the shoe and the ground.
What is the coefficient of friction (μ)?
A book resting on a table experiences two vertical forces. Name them.
What are weight and normal force?
If the net force on an object is zero, the object may still be doing this.
What is moving at constant velocity?
An object has a weight of 196 N. What is its mass?
20 kg
If an object's mass doubles, this quantity also doubles.
What is its weight (gravitational force)?
Why does a heavier box usually require more force to push across the floor?
A greater weight creates a larger normal force, leading to more friction.
A crate is pulled across the floor but does not move. What can be concluded about the length of the applied force and friction on the FBD?
They are equal in magnitude.
An object speeds up in the direction it is moving. What can be said about the net force?
The net force is in the direction of motion.
A 30 kg crate is pulled with a force of 180 N across a horizontal floor.
The friction force is 100 N.
Calculate the net force.
Fnet = 180 N − 100 N = 80 N forward
A student says, "Mass and weight are the same thing." Explain why this is incorrect.
Mass is the amount of matter in an object, while weight is the force of gravity acting on that mass.
A student places a book on a table and does not push it. Is friction acting? Explain.
No. There is no tendency for motion between surfaces, so friction is not needed.
An object moves to the right at a constant speed. A student draws a larger rightward force than leftward force. Explain the error.
What is that the horizontal forces must be equal because the net force is zero?
A student claims, "An object moving to the right must have a net force to the right." Explain why this statement is incorrect.
Objects can move at constant velocity with zero net force. A net force is only needed to change motion.
A 20 kg box sits on a level floor. The coefficient of friction is 0.40.
Calculate:
A bowling ball and a basketball are dropped side by side. Ignoring air resistance, which object experiences the greater gravitational force, and which accelerates faster?
The bowling ball experiences greater weight, but both accelerate at the same rate due to gravity.
Two identical boxes sit on different surfaces. One surface has a larger coefficient of friction. What does that tell you about the interaction between the surfaces?
The surfaces produce more frictional force for the same normal force.
A box slides across a rough floor after being given a push and released. Which horizontal force(s) should appear on the FBD?
What is friction?
A skydiver falls at terminal velocity. What is true about the net force?
The net force is zero.
A 40 kg box is pushed across a floor where μ = 0.30. The applied force is 200 N.
Calculate: