Unit 2

Question 1

Types of Force (in Newtons (N))

Answer 1

• Friction force → f
• Gravity force → Fg
• Applied force → Fa or Fapp
• Drag force → f (negative)
• Spring force → Fa or Fapp
• Magnetic force → F
• Tension force → F
• Buoyant force → F

Question 2

Contact forces

Answer 2

• Applied force
• Spring force
• Drag force
• Frictional force
• Normal force

Question 3

Non-contact forces

Answer 3

• Magnetic force
• Electric force
• Gravitational force

Question 4

Contact forces

Answer 4

interactions between objects that tough

Question 5

Non-contact forces

Answer 5

attract or repel, even form a distance

Question 6

Fundamental Forces

Answer 6

Forces of nature

• Electromagnetism
• Weak interaction / weak nuclear force
• Strong interaction / strong nuclear force
• Gravitation (weakest force)

Question 7

Gravitational (Function / Effect, Relative Strength, Range)

Answer 7

• Attractive force between matter
• 1
• Infinite

Question 8

Electromagnetic (Function / Effect, Relative Strength, Range)

Answer 8

• Like charges repel, opposites attract
• 10(36)
• Infinite

Question 9

Weak Nuclear (Function / Effect, Relative Strength, Range)

Answer 9

Involved in nuclear decay
10(29)
10(-18)

Question 10

Strong Nuclear (Function / Effect, Relative Strength, Range)

Answer 10

Holds the nucleus of an atom together
2 x 10(37)
10(-15)

Question 11

Newton’s Laws of Motion

Answer 11

1. An object remains at rest or in uniform motion unless acted upon by an external, unbalanced force → law of inertia
2. F (N) = m (kg) x a (m/s2) (force = mass x acceleration) or Fg (N) = m (kg) x a (m/s2) (force gravity = mass x acceleration (9.8))
3. When object A exerts a force on B, the force that B exerts on A is equal in magnitude

Question 12

What is friction?

Answer 12

A force that opposes motion between two surfaces in contact, and acts parallel to these surfaces
Friction always works in the direction opposite to the direction the object is moving (or intended motion)

Question 13

What affects friction?

Answer 13

The amount of friction depends on:
Roughness of the surface
Force pushing the surfaces together

Question 14

An electrostatic contact force

Answer 14

The surface of all objects is rough - even an object that feels smooth
Contact between hills and valleys in the surface causes electrostatic attractions, resulting in friction
Rough surfaces have more microscopic hills and valleys, producing more friction
Increasing the amount of force exerted by the object (by increasing the mass) increases the amount of friction

Question 15

What does not affect friction?

Answer 15

Surface area
- Apparent contact area ≠ true contact area
- More pressure for smaller contact area and vice versa
- P = Fg(N) (or 9.8)/Area (m2)
Speed of the object
- f = Fapp when there is no acceleration

Question 16

Types of Friction

Answer 16

There are two types of friction:

• Static Friction
  
  • The frictional force present before movement begins
  • Can have a range of values
• Kinetic Friction
  
  • The frictional force present when an object is moving
• The maximum static friction is usually higher than the kinetic friction between two objects
  
  • 0 ≤ fs ≤ max.
  • fk < fs maximum (almost always)
  • fk = constant

Question 17

Static Friction

Answer 17

Static friction occurs when the force applied to an object does not cause the object to move
In order to move something, you must first overcome the static friction between the object and the surface on which it is resting

Question 18

Kinetic Friction

Answer 18

Kinetic Friction occurs when force is applied to an object and the object moves
The net force on the moving object is the difference between the applied force and the frictional force.

Question 19

Types of Kinetic Friction

Answer 19

Sliding friction - pushing an object across a surface
Rolling friction - occurs between wheels and a surface
Fluid friction - opposes the motion of objects travelling through a fluid (also called drag force or air resistance) (fluid is also considered a liquid or a gas)

Question 20

Reducing Friction

Answer 20

Reduce the contact area by using rollers/ball bearings/wheels
Change the surfaces of the materials that are in contact by using lubrication like motor oil, wax or grease
Roll objects instead of sliding them
Create a cushion of air (hovercraft, air hockey table)

Question 21

How is friction determined?

Answer 21

Friction is based on the type of materials that are in contact
Every material has a coefficient of friction, which is a measure of how easily one material moves in relationship to another
A high coefficient mearns there is a lot of friction between the materials
Concrete has a very high coefficient of friction, while materials such as ice or Teflon (non-stick pans) have a very low coefficient

Question 22

General Friction Equation

Answer 22

friction (friction force) = μN (coefficient of friction x normal force)

Question 23

Review: Kinetic Friction

Answer 23

When an object slides, it experiences a frictional force. Kinetic friction force always opposes motion. It acts opposite the direction of motion.
Fkinetic = μkFN

Question 24

Review: Static Friction

Answer 24

When an object is at rest a static frictional force resists motion. The maximum static frictional forces are larger than the kinetic frictional forces.
Fstatic ≤ μsFN