Unit 4 Review

Question 1

What is a force?

Answer 1

A force is a push or a pull

Sometimes, it is obvious that a force has been applied, while other forces are less noticeable.

Question 2

What does a force cause?

Answer 2

A force causes objects to change their motion.

This can include changes in speed, direction, or shape.

Question 3

What is net force?

Answer 3

Net Force is the sum of all forces acting on an object.

It determines the overall effect of all the forces applied.

Question 4

How are forces measured?

Answer 4

Forces are measured in Newtons (N).

The Newton is the standard unit of force in the International System of Units (SI).

Question 5

What are the three rules for adding forces?

Answer 5

1. Add forces in the same direction.
2. Subtract forces in opposite directions
3. Forces not in the same direction or in opposite directions cannot be directly added together

This means that if two forces are acting towards the same point, their magnitudes can be summed.

Question 6

True or False: Forces not in the same direction or in opposite directions can be directly added together.

Answer 6

False

Forces that are not aligned cannot be summed directly.

Question 7

What type of quantities are forces?

Answer 7

Forces are vector quantities.

This means they have both magnitude and direction, similar to displacement.

Question 8

In a free-body diagram, what does the size of the arrow represent?

Answer 8

The magnitude of the force

Question 9

In a free-body diagram, what does the direction of the arrow indicate?

Answer 9

The direction that the force is acting

Question 10

What is labeled on each force arrow in a free-body diagram?

Answer 10

The exact type of force

Question 11

Fill in the chart with the type of force and what category it belongs to.

The symbols have been left to help you.

Answer 11

Question 12

What is the symbol for Air Resistance Force?

Answer 12

F_air

Question 13

What type of force is Applied Force represented by?

Answer 13

F_app

Question 14

Which type of force is represented by the symbol Fs?

Answer 14

Spring Force

Question 15

Name three types of action-at-a-distance forces.

Answer 15

• Gravitational Force (F_g)
• Electrical Force (F_E)
• Magnetic Force (F_m)

Question 16

What are free-body diagrams used for?

Answer 16

To show the relative magnitude and direction of all forces acting on an object.

Free-body diagrams help visualize the forces in physics problems.

Question 17

Fill in the blank: Free-body diagrams illustrate the _______ and direction of forces.

Answer 17

magnitude

Question 18

A book is at rest on a table top.

Create a free-body diagram to show the forces acting on the book.

Answer 18

Question 19

What is normal force?

Answer 19

The force that surfaces exert to prevent solid objects from passing through each other

Question 20

A force is applied to the right to drag a sled across loosely packed snow with a rightward acceleration. 

Create a free-body diagram showing the forces involved.

Answer 20

Question 21

A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance.

What would a free-body diagram for this situation look like?

Answer 21

Gravity pulls down on the squirrel while air resistance keeps the squirrel in the air for a while. Constant velocity does not mean the object is not moving.

Question 22

What is the net force of the free-body diagram below?

Answer 22

400 N (north)

Question 23

The force that opposes the sliding motion of two surfaces that are touching each other is called what?

Answer 23

Friction

Friction comes from the Latin word fricare meaning “to rub”

Question 24

Friction occurs because the surface of any object is _______.

Answer 24

rough

Even surfaces that feel smooth are covered with microscopic hills and valleys

Question 25

When two surfaces are in contact, microscopic hills and valleys of one surface stick to the tiny hills and valleys of the other surface. What is this contact known as?

Answer 25

microwelds ## Footnote microwelds cause friction

Question 26

What is static friction?

Answer 26

When a force is applied to an object but does not cause the object to move ## Footnote The object does not move because the force of static friction balances the force applied.

Question 27

If static friction is occuring, what is the net force?

Answer 27

zero ## Footnote The word *static* means "not moving."

Question 28

What is kinetic friction?

Answer 28

the friction between moving surfaces

Question 29

After static friction disappears when an object starts moving, what type of fricton immediately occurs after?

Answer 29

kinetic friction (rolling or sliding)

Question 30

The amount of kinetic friction between two surfaces depends in part on how the surfaces _____.

Answer 30

move

Question 31

What are two types of kinetic friction?

Answer 31

* Sliding Friction * Rolling Friction

Question 32

What type of friction opposes the motion of two sliding surfaces sliding past one another?

Answer 32

sliding friction

Question 33

Sliding friction is caused by __________ constantly breaking and forming as objects _____ past one another.

Answer 33

microwelds, slide

Question 34

Where does rolling friction occur?

Answer 34

between the bottom of a wheel and the ground

Question 35

True or false: Sliding friction is helpful when driving.

Answer 35

False ## Footnote Rolling friction is helpful when driving

Question 36

What type of friction is also known as traction?

Answer 36

Rolling friction

Question 37

Is rolling friction or sliding friction easier to overcome?

Answer 37

Rolling friction ## Footnote In rolling motion, only a small area of the object is in contact with the surface at any time, reducing resistance

Question 38

What are the four fundamental forces in the universe?

Answer 38

* Electromagnetic * Strong nuclear force * Weak nuclear force * Gravity

Question 39

True or false: At this moment, you are exerting an attractive force on everything around you.

Answer 39

True ## Footnote Even the planet Jupiter, which is millions of kilometers away, is being attracted by your gravitational force

Question 40

Define gravity.

Answer 40

an attractive force between any two objects that depends on the masses of the objects and the distance between them

Question 41

Provide the law of Universal Gravitation.

Answer 41

F = G(m₁m₂ / d²) ## Footnote * F = gravitational force between the objects (in Newtons) * G = universal gravitational constant * m₁ and m₂ = masses of the two objects (in kilograms) * d = distance between the centers of the two objects (in meters)

Question 42

All ________ is affected by gravity.

Answer 42

matter

Question 43

What are the two ways gravitational force can either increase or decrease?

Answer 43

* change in mass * change in distance ## Footnote more mass = more gravitational force closer distance = more gravitational force

Question 44

Nathaniel's Argument: ``` No matter how far apart two objects are, the gravitational force between them never completely goes to zero. ``` Camden's Argument: ``` Wow! You are dumb as rocks. Only the objects on Earth pull eachother with gravitational force, meaning that objects far away have a gravitational attraction of zero. ``` Which student is correct?

Answer 44

Nathaniel ## Footnote Because the gravitational force between two objects never disappears, gravity is called a long-range force

Question 45

A region of space that has a physical quantity (such as force) at every point is also called what?

Answer 45

a field ## Footnote Because objects do not have to be in contact, gravity is sometimes discussed as a field

Question 46

What is the strength of the gravitational field near Earth's surface?

Answer 46

9.8 N/kg

Question 47

Define weight.

Answer 47

The gravitational force exerted on an object ## Footnote The symbol for weight is F_g

Question 48

True or false: The weight of an object on Earth is equal to the force of Earth's gravity on the object.

Answer 48

True ## Footnote The weight of an object is exactly the gravitational force Earth exerts on the object.

Question 49

Provide the equation for weight.

Answer 49

weight (N) = mass (kg) x gravitational strength (N/kg) ## Footnote The weight of an object usually is the gravitational force between the object and Earth

Question 50

True or false: Weight and mass are the same.

Answer 50

False ## Footnote Weight is a force while mass is a measure of the amount of matter an object contains

Question 51

As mass increases, so does ______.

Answer 51

weight

Question 52

Define Newton's first law of motion.

Answer 52

An object moving at a constant velocity keeps moving at that velocity unless an unbalanced net force acts on it

Question 53

What is the tendency of an object to resist any change in its motion?

Answer 53

inertia ## Footnote An object will keep moving at the same speed and in the same direction unless an unbalanced force acts on it.

Question 54

What is Newton's First Law of Motion sometimes called?

Answer 54

the law of inertia

Question 55

Define Newton's second law of motion.

Answer 55

The acceleration of an object (which can be calculated from a specific equation) is in the same direction as the net force on the object

Question 56

Provide the Second Law of Motion equation.

Answer 56

a = F_net / m ## Footnote 1. acceleration = meters per second² 2. net force = in newtons 3. mass = in kilograms

Question 57

Define Newton's third law of motion.

Answer 57

When one object exerts a force on a second object, the second one exerts a force on the first that is equal in strength and opposite in direction ## Footnote These forces are sometimes called the action and reaction forces

Question 58

In a car crash, any passenger not wearing a seatbelt continues to move forward at the same speed the car was traveling? What is this due to?

Answer 58

inertia

Question 59

What describes the fall of an object on which only the force of gravity is acting?

Answer 59

free fall

Question 60

The acceleration of a falling object (in free fall) is given the symbol __ and is sometimes called the acceleration of _______.

Answer 60

g, gravity

Question 61

Define air resistance.

Answer 61

A friction-like force that opposes the motion of objects that move through the air

Question 62

What three things does air resistance depend on?

Answer 62

* Size * Shape * Speed of an object

Question 63

The reason why some objects fall slower than others is due to which force?

Answer 63

air resistance

Question 64

The highest speed a falling object will reach is also known as what?

Answer 64

terminal velocity

Question 65

As an object falls, the downward force of _______ causes the object to accelerate. However, as an object falls faster, the upward force of ____________ increases, which causes the ___ force on a sky diver to eventually reach zero.

Answer 65

gravity, air resistance, net

Question 66

True or false: If the net force on an object is zero, so is the object's acceleration.

Answer 66

True

Question 67

The motion of an object when gravity is the only force acting on it is also called what?

Answer 67

free fall ## Footnote In free fall, the object accelerates downward at a constant rate (9.8 m/s² if the object was near earth's surface)

Question 68

The sensation when there is no support force acting on your body, making you feel as though you have no weight is also known as what?

Answer 68

weightlessness ## Footnote Weightlessness occurs in situations such as free falling

Question 69

List two examples of situations where freefalling takes place.

Answer 69

* Astronauts orbiting Earth in a space station * A vaccum chamber experiment ## Footnote 1 - The spacecraft and astronauts are in free fall around Earth, creating the sensation of weightlessness 2 - Objects like a feather and a bowling ball dropped inside a vaccum chamber fall freely without air resistance

Question 70

The momentum of an object doesn't change unless its ____, _______, or both change.

Answer 70

mass, velocity

Question 71

True or false: Momentum can be transferred from one object to another.

Answer 71

True

Question 72

What does the law of conservation of momentum state?

Answer 72

If a group of objects exert forces only on each other, their total momentum doesn't change

Question 73

True or false: In orbit, the weight of astronauts becomes zero.

Answer 73

False ## Footnote In orbit, the weight of astronauts is about 90 percent of what it would be on Earth's surface. It decreases, but does not become zero.

Question 74

A rocket lifting up after firing its thruster is an example of...

Answer 74

action and reaction forces

Question 75

What force is necessary to move an object with a mass of 10kg at a rate of 47 m/s²?

Answer 75

470 N

Question 76

What causes some objects to fall slower than others?

Answer 76

air resistance

Question 77

What keeps the satellite moving in a circular orbit?

Answer 77

gravity

Question 78

What is the net force on a sky diver falling with a constant velocity of 10 m/s downward?

Answer 78

0N because the acceleration is 0 at a constant velocity

Question 79

``` An applied force of 20N is used to accelerate an object to the right across a frictional surface. The object encounters 8N of friction. Use the diagram to determine the normal force, the net force, the coefficient of friction ("mu") between the objects and the surface, the mass, and the acceleration of the object. Neglect air resistance ``` m = ____________ a = _____________ F_net = _____________ µ = ______________ F_N = ___________

Answer 79

m = 31.63 kg a = 0.38 m/s² F_net = 12 N µ = 0.03 F_N = 310 N

Question 80

``` A rightward force is applied to a 621-g object to move it across a rough surface at constant velocity. The coefficient of friction between the object and the surface is 0.088. Use the diagram to determine the gravitational force, normal force, applied force, frictional force, and the net force. (Neglect air resistance). ``` m = ___________ a = ___________ F_net = ___________ µ = ___________ F_g = ___________ F_N = ___________ F_app = ___________ F_friction = ___________

Answer 80

m = 0.621 kg a = 0 m/s² F_net = 0 N µ = 0.088 F_g = 6.09 N F_N = 6.09 N F_app = 0.54 N F_friction = 0.54 N