Dynamics Test

Question 1

Mass

Answer 1

the amount of matter in an object

-a SCALAR quantity
-units are kg
symbol m

Question 2

Weight

Answer 2

the force of gravity on an object

• a VECTOR quantity
• units are N
• Fg

Question 3

Force

Answer 3

a push or a pull

-a VECTOR quantity
F = ma

Question 4

Newton

Answer 4

the SI unit for Force

Question 5

Inertia

Answer 5

a property of matter that causes an object to resist changes in its state of motion

(it is directly proportional to the mass of the object

Question 6

Kinetic Friction

Answer 6

the force that acts between moving surfaces

in a situation of kinetic friction, the force of static friction is not able to balance the applied force, so motion occurs

Question 7

Static Friction

Answer 7

the force that prevents an object at rest from starting to move

Question 8

Friction Comparison: Static & Kinetic

Answer 8

the magnitude of the force of Fk is NEVER GREATER than the maximum of the force of Fs

μk < μs

Question 9

Friction

Answer 9

a force that is present in almost all-real life situations, in which it acts parallel to the common surface between 2 objects, resisting between them

Question 10

Coefficient of Static Friction

Fs ≤ μsFN

Answer 10

μs = use when object is at rest

—> where μs is a proportionality constant

Question 11

Coefficient of Kinetic Friction

Fk = μkFN

Answer 11

μk = use when object is sliding

—> where μk is a proportionality constant

Question 12

What are the 4 Fundamental Forces?

Answer 12

1. Gravitational Force
2. Electromagnetic Force
3. Strong Nuclear Force
4. Weak Nuclear Force

Question 13

Gravitational Force

Answer 13

• known as “force of gravity” or “weight”
• attraction ONLY
• acts between all objects in the universe
• weak force but long range

Question 14

Electromagnetic Force

Answer 14

• caused by electrical charges
• most common force (light, electricity)
• strong force and long range

Question 15

Strong Nuclear Force

Answer 15

• holds protons and neutrons together

- strongest force but very short range

Question 16

Weak Nuclear Force

Answer 16

• responsible for radioactivity

- strong force but very short range

Question 17

The mass and weight of a person are measured on Earth and then on Mars. How will the values of mass and weight for the person compare at the 2 locations?

Answer 17

The mass on Mars will be the same as on Earth, but the weight will be less. Mars is not as massive as the Earth, therefore, Fg will be smaller.

Question 18

Newton’s First Law of Motion

Answer 18

An object at rest will stay at rest unless acted on by an unbalanced force

An object in motion will continue with constant speed and direction unless acted on by an unbalanced force

EX. a soccer ball is sitting at rest. it takes an unbalanced for of a kick to change its motion

Question 19

A marble, a golf ball, and a bowling are all dropped off of the roof of the school at the exact same time. The three objects have different masses. The marble is the least massive; the bowling ball has the most mass. Which will reach the ground first?

Answer 19

All three will reach the ground at the same time. The gravitational force (or weight) of all three is different, but the acceleration is the same.

Question 20

Newton’s Second Law of Motion

Answer 20

an object accelerates relative to the force applied and in the direction of the force

(the greater the force applied, the greater the distance travelled and the higher the speed)

• the acceleration is directly proportional to the net force, but is inversely proportional to the mass

EX. a tennis player hitting a tennis ball

Question 21

Newton’s Third Law of Motion

Answer 21

For every force exerted by one object onto a second object, there is a force exerted by the second object onto the first that is equal in magnitude but opposite in directions. (action/reaction forces)

FOR EVERY ACTION, THERE IS AN EQUAL BUT OPPOSITE REACTION

EX. when the air from a balloon is released the air rushes downwards as the balloon is forced upwards

Question 22

In order to understand Newton’s 3rd Law, you must understand Action-Reaction pairs. Based on the definition of these force pairs why don’t they cancel each other out on a FBD?

Answer 22

An FBD only shows forces that act on one object. Action-Reaction forces act on different objects.

Question 23

1st Law of Motion Examples:
Inertia of a passenger makes her feel like she is being thrown ________________________ when the direction of the acceleration of the bus is opposite to the direction of its velocity.

Answer 23

FORWARD

Question 24

1st Law of Motion Examples:
Inertia of a passenger makes her feel like she is being pushed _______________________ when the acceleration of the vehicle is in the same direction as its velocity.

Answer 24

BACKWARD

Question 25

1st Law of Motion Examples:

What happens to the motion of the passenger when the bus goes around a curve?

Answer 25

Inertia of passenger makes her feel like she is being thrown inward or outward (depending on the direction of the curve) when the direction of the velocity changes as the vehicle accelerates around a curve