Module 1 Chp 2 Forces and Shape + Chp 3 + Chp 4 + Chp 5

Define "drag."

Objects experience friction when they move through a liquid or a gas.

What does weight equal ??

Weight only equal to gravitational force

Define "upthrust."

The upward force from a liquid/gas that makes some things float.

Define “weight.”

The gravitational force on an object

Define “tension.” 

The force in a stretched material

OBJQ

Define "friction."

The force that opposes the motion of one material sliding past another

Define “thrust.”

The forward force from an engine

Define “air resistance.”

An object moving through air experience a force that opposes its movement

What is a balanced force?

When resultant force = 0, so a = 0

What are 2 scenarios that a = 0?

If an object is originally at rest, it will continue at rest 

If object move with certain velocity, will move with same constant velocity, so a = 0rest.

What is Newton’s first law?

-There is no net external force acting on an object; if an object is initially at rest, it will continue to rest. If an object moves with a certain velocity, it will continue moving with the same constant velocity. So there is not acceleration.

Explain the relationship between thrust and drag.

Thrust>Drag (Speeding up)

Thrust<Drag (Slow down)

What is Newton Second Law

he resultant force acting on an object is equal to the product of mass and acceleration of the object

F = ma

F = resultant force

m = mass 

a = acceleration

Downward arrow reaction or action?

action

Upward arrow reaction or action?

Normal reaction

When does an action-reaction pair occur?

It occurs when 2 objects interact with each other. (not only on single object)

What is Newton’s Third Law?

Whenever 2 objects interact to each other, the force exerted by the first on the second is equal in magnitude and opposite in direction to the force exerted by the second on the first. This is an action-reaction pair.

When does free fall occur?

When there is no air resistance

What are the other names for free fall? And its symbol

Acceleration due to gravity 

Acceleration of free fall

Symbol = g

What is the upward and downward reaction with gravity and speed?

Upward→against gravity→speed decrease

Downward→same direction with gravity→speed increase

What are free fall equations?

What are the relationships between the same mass and different force and the same force and different masses?

Same mass

F1 > F2

a1 > a2

accelration (a) directly proportional to F (force)

Same force

m1 < m2

a1 > a2

acceleration (a) inversly proportional to mass.

Weight equation?

W = mg

Weight = mass x gravitational field strength

OBJQ 

What are weight, location, gravitational field strength, and mass relation?

Weight depends on mass and gravitational field strength. Different location→different value of gravitational field strength. Greater the mass of location (Planets)→larger gravitational field strength

What is Earth's gravitational field strength?

10 N/kg (9.8 N/kg)

Which apparatus can we use to measure mass?

Mass=Electric balance or digital balance 

Force, weight = spring balance or newton meter

OBJQ

Why does weight change but mass doesn’t when location changes?

Since w=mg, mass doesn’t depend on location, but weight does: gravitational field strength ‘g’ can change according to the location. Therefore, the weight of a body may change when its location changes.

OBJQ

What factors does air resistance depend on?

Speed→The faster they move, the greater the drag force opposing their motion becomes

Shape→ Streamlined smooth surface experience less air resistance. Larger surface area, the more air resistance it experiences.

What forces does that object failing through air experience?

Weight, and drag

Explain the falling-through-air experience.

• At first, it has weight only and no air resistance. 

• The resultant force is downward, so it has acceleration.

•  There is air resistance. Air resistance increases with increasing speed, and the resultant force becomes decreased. Acceleration also decreases. 

• Eventually air resistance is equal to its weight and 2 forces are balanced and the resultant force becomes zero. 

• There it falls with terminal velocity (Constant velocity)

Explain the process after the parachute happens.

• After the parachute opened, air resistance greatly increased. 

• Air resistance greater than weight. 

• Then air resistance decreases with the decreasing speed. 

• Eventually, air resistance is equal to its weight, 2 forces are balanced, and the resultant force becomes zero. 

• So parachutists fall with low terminal velocity.

OBJR + FAQ

What is thinking distance/reaction time?

When a driver suddenly sees an object blocking the way ahead, it takes time for him or her to respond to the new situation before any action, such as braking. It is called reaction time.

OBJQ + FAQ

What does thinking distance depend on?

(i) Driver’s condition (use of alcohol or drug)

(ii) Tiredness of the driver 

(iii) Poor visibility (fog)

(iv) Speed of car

OBJQ + FAQ

What does breaking distance depend on?

(i) Road’s condition (let friction due to wet or icy) 

(ii) Tier’s condition (not enough to grip the road’s surface) 

(iii) Speed of car

OBJR

What is stopping distance?

Thinking distance + Breaking distance

FAQ

Define elastic behavior.

When applied force is removed from an object, the ability to return to its original form is called "elastic behavior" or "elastic object." 

What is an extension equation?

Extension = new length - original length

 x or e = L - L₀

What is the original length equation?

Original length = new length - extension 

L₀ = L - x or e

What is Hooke’s Law?

As long as the elastic limit of object is not exceeded, the extension is directly proportional to its applied force

2 equations of Hooke’s Law?

F = kx 

k = F/x (in normal calculation and load-extension graph) 

k = 1/gradient (extention-load graph)

F = applied force 

k = spring constant, Hooke’s constant 

x = extension

How to prove that a graph obeys Hooke’s Law? 

-The graph is a straight line & passing through the origin.

Why does a curve happen in the graph of the extension-load graph?

When a student doesn’t check whether the spring goes back to its original length or not.

Label which part follow Hooke’s law, elastic limit and limit of proportionality

FAQ

What is a moment of force?

Turning effect of force about a pivot.

OBJQ

Equations of a moment?

moment = force x perpendicular distance from pivot 

Moment = f d sin θ

What are directions of moment?

Clockwise and Anti-clockwise

How to prove an object is balanced in a seesaw?

Total anti-clockwise moment = total clockwise moment

What is the principle of moments?

If an object is in equilibrium, total clockwise moment is equal to total anti-clockwise moment

FAQ

What are the conditions for equilibrium?

Total anti-clockwise moment = total clockwise moment (or) Resultant moment = 0

Total upward force = total downward force (or) 

The resultant force = 0