revision: Physics - Topic 1

IMPORTANT: I will not post the link to this blog anywhere now.

This is because apparently we can all fail IGCSE if I give you resources and stuff...I don't really understand it but yeah...better safe than sorry...So...please after this post. If you share the link do it privately...I might add a password in the future...but I'll tell you all if I do.

Thank you.

Anyone who fails to follow...I'm afraid I'll have to close all access to this site for everyone :(
I don't wanna fail... ._.
-.- Who does?
Sorry. And thanks xD

-mirunae

1a) Units

1.1 - use the following units: kilograms (kg), meter (m), meter/second (m/s), meter/second2 (m/s2), Newton (N), second (s), Newton per kilogram (N/kg), Newton meter (Nm)

second (s) is used for time.
meter (m) is used for a length or distance.
kilograms (kg) is used for mass.

Okay, those were the simple ones...are you ready? :D

meters/second (m/s) is used for speed or velocity.
meters/second² (m/s²) is used for acceleration.

Newton (N) is used for force (or weight)
Newton per kilogram (N/kg) is how much force for every kilogram. (Gravitational field strength)
Newton meter (Nm) is the unit for moment (M = F x d where F is force measured in Newtons or 'N' and d  is distance measured in meters or 'm' therefore, moment or 'M' is measured in 'Newton meters' or 'Nm')

1b) Movement and Position

1.2 - plot and interpret distance-time graphs.

The blue line shows the constant speed of something moving away from the starting point. The red line then shows the object being stationary (at rest). The green line then shows the object moving at a constant speed back to the starting point by the negative gradient.

With distance time graphs, we can tell the displacement of an object (the distance in a particular direction) of an object. If the gradient is positive, the object is moving away from the start. If the gradient is negative it to moving towards the starting point.

(REMEMBER -> You write with a pen, therefore, it is a piece of stationery. Stationary means to STAPH!)

1.3 - know and use the relationship between average speed, distance moved and time:
v = d/t
average speed = distance moved/time

v = velocity (m/s)
d = distance (m)
t = time (s)

You might see velocity in km/h, distance in km and time in hours sometimes but I think the ones above are more common...

Anyways, remember the triangle?

(REMEMBER -> Don't Smoke Tobacco (Distance = Speed x Time) but my friend likes the one 'Dumb, Stupid Teachers' better!)

1.4 - describe experiments to investigate the motion of everyday objects such as toy cars or tennis balls.

1.5 - know and use the relationship between acceleration, velocity and time: 

acceleration = change in velocity/time taken
a = (v - u)/t

Acceleration is the rate of change of an object's velocity. It is vector as the direction and size are both important. It is measures in meters/second² (m/s²) 

1.6 - plot and interpret velocity-time graphs

The gradient of a velocity-time graph gives us the acceleration. 
The area below the graph gives us the distance.
(Wait, just to be certain, you guys DO know that velocity and speed are the same thing except that speed is a scalar quantity and velocity is a vector quantity giving a value and a direction, right?)

1.7 - determine acceleration from the gradient of a velocity-time graph

Like shown in the diagrams above, the gradient is the change in y divided by the change in x.
Since on the y-axis we have the speed, and on the x-axis we have the time. The gradient on the speed-time graph or velocity-time graph becomes the change in speed divided by the change in time (or the time taken) and oh, look...

 So...the gradient of the velocity-time (or speed-time) graph gives us the acceleration.

1.8 - determine the distance traveled from the area between a velocity-time graph and the time axis


Well, I don't know how to explain...so I'll give an example!

1c) Forces, movement, shape and momentum

1.9 - describe the effects of forces between bodies such as changes in speed, shape or direction

A forces is a push, a pull or a twist that acts on an object. It can change the way things move making them move slower or faster and changing the direction of the movement. It can also change the shape of things.

So...
It can:

• change the direction of an object
• change the velocity of an object (accelerate it and decelerate it)
• change the shape of an object

1.10 - identify different types of force such as gravitational or electrostatic

The different types of forces are:

weight (gravitational attraction) - a force that acts on an object due to gravity.

friction - a force the opposes motion

drag (air resistance/water resistance) - a force that opposes motion in between the substance (air/liquid) it is moving through.

upthrust - the upward force that acts upon an object.

magnetic - the force that is exerted by and acts upon magnets and magnetic things.

electrostatic - the force between electrically charged objects.

nuclear - the force caused by nuclear.

tension - the force of an object being stretched or pulled.

Let me know if I missed any out ;)

1.11 - distinguish between vector and scalar quantities

(Don't ask me why sausages is up there, I got this list from my teacher...but you get the idea, right?)

1.12 - understand that force is a vector quantity

From this diagram you can tell two things.
The first is that the arrow for weight is larger than the arrow for air resistance. This means that the weight is larger than the air resistance. (The object is accelerating downwards)
The second is the direction the arrows are pointing. Weight is a downwards force which air resistance is an upwards force.
With both a value and a direction, force is therefore a vector quantity.

It can be measured using a newton meter.

1.13 - find the resultant force of forces that act along a line

When there is no resultant force, the forces are balanced.
When there IS a resultant force, the forces are unbalanced.

(REMEMBER-> Forces are vector quantities so they have both a value/magnitude AND a direction)

When there is a resultant force and the forces are unbalanced, the object is accelerating or decelerating. This is Newton's 2nd Law.

1.14 - understand that friction is a force that opposes motion

Friction is a force that opposes motion and acts in the opposite direction. Each acting force has a reacting force - this is Newton's third law.

1.15 - know and use the relationship between unbalanced force, mass and acceleration:

force = mass x acceleration
F = m x a

This equation shows that the acceleration of an object is proportional to the force acting upon it. The greater the force the greater the acceleration. Also, rearranging the equation tells us that the larger the mass of the object the smaller the rate of acceleration too.

This is what that dude Newton did...
And what he came up with...
1. When there is no resultant force and the forces are balanced, the object is stationary or moving at a constant speed.
2. When there is a resultant force and the forces are unbalanced, the object is accelerating or decelerating proportional to the force acting on it.
3. Every acting force acting on an object has a reacting force. (action = reaction)

1.16 - know and use the relationship between weight, mass and g:

weight = mass x g
W = m x g

1.17 - describe the forces acting on falling objects and explain why falling objects reach a terminal velocity.

LOL The diagrams ><><><>< BAHAHA Thank my phone.

1. I'm stupid and decide to jump off a plan with only socks and diapers on.  Okay, I jump of the plane...
At first, the only force is weight...as you can see. And since there is an obvious unbalanced force, I accelerate.

2. As I continue to fall and accelerate, my speed increases. When my speed increases, air resistance also increases and so the resultant force gets less and less until ....DAN DAN DAN... I fall at terminal velocity! There is no resultant force and the forces are balanced.

3. I decide that I don't actually want to die...so I open my parachute! (I can't die, I have to finish writing this for you guys)  The surface area increases and so air resistance increases. The forces are unbalanced again and so I decelerate. This is due to the upwards force (the air resistance) being larger than the downwards force (the weight).

4. Of course, now that I'm decelerating, there is less air resistance and so the forces are balanced again. Now, I am travelling safely at terminal velocity again too!

Okay, now that I'm safely on the ground (oh, look, I've grown up too!) with all my clothes on...
My weight is balanced by the reaction force of the ground. There is no resultant so I'm safely on the ground (my speed is zero).

1.18 - describe experiments to investigate the forces acting on falling objects, such as sycamore seeds or parachutes.

1.19 - describe the factors affecting vehicle stopping distance including speed, mass, road condition and reaction time.

Stopping distance = braking distance + thinking distance

Stopping distance - The total distance it takes to stop.
Braking distance - The distance is takes for the vehicle to stop after the brakes are applied.
Thinking distance - The distance it takes before the driver applies the breaks (during the reaction time)

Reaction time - The time is takes the driver to apply the breaks after seeing the problem.

Thinking distance can be increased by -> use of drugs, the weather, tiredness, etc.
Braking distance can be increased by -> bad tire conditions, high speed of car, etc.

1.25 - know and use the relationship between the moment of a force and its distance from the pivot:

moment = force x perpendicular distance from the pivot
M = F x d


The moment of a force is its 'turning effect'

1.26 - recall that the weight of a body acts through its center of gravity

Everything has a center of gravity in which it's weight acts upon. Remember, weight is the gravitational force of attraction of the earth acting upon an object giving it's weight.

Don't really know how to explain.

1.27 - know and use the principle of moments for a simple system of parallel forces acting in one plane.

Usually, the question will ask you to find a missing value of F or d from either side, all you have to do it substitute the numbers in.

1.28 - understand the the upward forces on a light beam, supported at its ends, vary with the position of a heavy object placed on the beam.

Use the equation above, to calculate the moments :)

1.29 - describe experiments to investigate how extension varies with applied force for helical springs, metal wires and rubber bands

Extension - The increase in length when something is stretched. You can measure it or calculate it.


1.30 - understand that the initial linear region of a force-extension graph is associated with Hooke's law.

Hooke's Law - the force is directly proportional to the extension. It only applies if you don't stretch the spring too much. (over the limit)

1.31 - describe elastic behavior as the ability of a material to recover its original shape after the forces causing deformation have been removed.

PLASTIC - will not return to its original extension when force is removed and will keep its shape.
ELASTIC - will return to it's original extension when force is removed.