Unit 2 Flashcards
Types of Force (in Newtons (N))
- 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
Contact forces
- Applied force
- Spring force
- Drag force
- Frictional force
- Normal force
Non-contact forces
- Magnetic force
- Electric force
- Gravitational force
Contact forces
interactions between objects that tough
Non-contact forces
attract or repel, even form a distance
Fundamental Forces
Forces of nature
- Electromagnetism
- Weak interaction / weak nuclear force
- Strong interaction / strong nuclear force
- Gravitation (weakest force)
Gravitational (Function / Effect, Relative Strength, Range)
- Attractive force between matter
- 1
- Infinite
Electromagnetic (Function / Effect, Relative Strength, Range)
- Like charges repel, opposites attract
- 10(36)
- Infinite
Weak Nuclear (Function / Effect, Relative Strength, Range)
Involved in nuclear decay
10(29)
10(-18)
Strong Nuclear (Function / Effect, Relative Strength, Range)
Holds the nucleus of an atom together
2 x 10(37)
10(-15)
Newton’s Laws of Motion
- An object remains at rest or in uniform motion unless acted upon by an external, unbalanced force → law of inertia
- 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))
- When object A exerts a force on B, the force that B exerts on A is equal in magnitude
What is friction?
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)
What affects friction?
The amount of friction depends on:
Roughness of the surface
Force pushing the surfaces together
An electrostatic contact force
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
What does not affect friction?
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
Types of Friction
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
Static Friction
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
Kinetic Friction
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.
Types of Kinetic Friction
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)
Reducing Friction
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)
How is friction determined?
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
General Friction Equation
friction (friction force) = μN (coefficient of friction x normal force)
Review: Kinetic Friction
When an object slides, it experiences a frictional force. Kinetic friction force always opposes motion. It acts opposite the direction of motion.
Fkinetic = μkFN
Review: Static Friction
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
