Result for SBA #12

Below is the table of results for SBA #12:

V/cm3	50.0	45.0	40.0	35.0	30.0	25.0	20.0	15.0
t1/s	0	13.06	26.7	42.19	58.37	75.66	94.38	115.88
t2/s	0	13.94	28.4	44.13	60.84	78.75	98.26	126.62
t/s

Results for SBAs #10 and 11

SBA #10

A = 0.52A
B = 0.26A
C = 0.16A
D = 0.08A
E = 0.52A

SBA #11

Number of Throws	Undecayed Atoms
1	47
2	20
3	12
4	6
5	4

The results for SBA #12 are not good so that will be done again.

Force, Mass and Weight

Force

A force can be defined as a push or a pull. It can change the size, shape or motion of a body. There are several different types of forces, some of which are:

• Gravitational force
• Electrical force
• Magnetic Force
• Nuclear force
  

Measuring Force

The spring balance is used to measure force. The spring balance is based on the fact that the extension of the spring is proportional to the force applied. The unit of force is the newton (N).

Stretching a Spring

We hang a wire spring from a retort stand. A pointer and a small pan are hung at the bottom of the spring. We set up a scale, marked in millimetres vertically by the side.

We add a series of small, equal weights which stretch the spring. We measure the extension i.e. the extra length, of the spring. Typical results are shown in the table below:

Force F/N	0	1.0	2.0	3.0	4.0	5.0
Extension e/cm	0	1.6	3.2	4.8	6.4	8.0

If a graph of extension against load is plotted, a straight line passing through the origin will be obtained. This means that extension if proportional to the load.

Elastic Limit of Springs

If we remove the weights the spring contracts to its original length. However, if we continue to add greater weights, eventually the spring stretches by different amounts. At this point, the extension is no longer proportional to the load.

When we remove the lager weights the spring does not return to its original length. We have gone beyond the elastic limit of the spring. The new graph looks like this:

Hooke's Law

Hooke's law states that the extension of a spring is directly proportional to the force applied, provided the elastic limit has not been exceeded.

We can obtain similar graphs for elastic bands and for straight metal wires. Elastic bands need smaller forces for a measurable extension and metal wires need much greater ones. 

The following video explains more on Hooke's Law:

Mass and Weight

Mass

The mass of an object is the measure of the amount of matter it contains. The mass of an object is also a measure of a resistance to a change in its motion. This resistance is known as the inertia of the body.

We measure mass using a triple beam balance as shown in the picture below. The unit of mass is the kilogram (kg). The mass of an object is constant everywhere.

Weight

The weight of an object is the force of gravity on the object. It acts towards the centre of the earth.

We measure weight using a spring balance as shown in the diagram below. The unit of weight is the newton (N). A mass of 1 kg has a weight of approxiamtely10N on earth. The weight of an object changes is the force of gravity changes.

In outer space there is no gravity, a 1kg mass has no weight. On the moon, where the gravity is about a sixth i.e. 1/6 that on the earth, a mass of 1 kg has a weight of about 1.6 N, as shown in the calculation below

Motion 2

Equations of Uniformly Accelerated Motion

When we have objects moving with a constant acceleration we can also use certain equations to solve problems. In these equations we use the following symbols:

You should be able to recall ALL of the following equations:

This implies that

The above equation can be rewritten as:

You should also know ALL of the following:

Falling Objects

We can drop a large stone and a piece of chalk from a height of 3 or 4 metres and they land simultaneously. However, a stone will reach the ground faster than a piece of paper. If the stone and paper are allowed to fall in a vacuum they fall together.

When objects fall in the air the resistance of the air has a greater effect on the light objects, such as the paper, than on heavy ones, such as the stone. Fluid friction (or viscous drag) always opposes the fall of objects through fluids, i.e. liquids and gases.

Acceleration due to Gravity

If the effects of air resistance are eliminated, or negligible, then all objects fall with the same acceleration. This is called acceleration due to gravity, g.

The acceleration due to gravity has slightly different values in different parts of the world but all values are about 9.81 metres per second squared. We often take g as 10 metres per second squared, as a convenient approximation.

SBAs

Note that all of your SBAs are posted to the blog. Try to get them all through. I will be collecting your books on Thursday, 27th March, 2014 to mark up to wherever you are at. You will collect your books the same day so you can finish up your labs.

The official deadline for your physics SBA books is next week Wednesday i.e. Wednesday, 2nd March, 2014. Try to be all through.

We are nearing the end so put in the effort. It will soon be all over.

Good luck!

Motion

Vectors and Scalars

Vector quantities have both size and direction. Examples of vector quantities are velocity, displacement, acceleration and force.

Scalar quantities have size but no direction. Examples of scalar quantities are speed, distance and mass.

Distance and Displacement

When total distance travelled by and object is calculated, we take no account of the direction in which it travels. Distance is scalar.

Displacement is defined as the distance moved in a particular direction. It id a vector quantity. The diagram represents a man walking on a football field. He starts at P and walks 50m due east - a displacement of 50m. He then walks 50m due north. 

His total distance travelled would be the distance from P to Q to R. However, his displacement would be the direct distance between his starting point and ending point, i.e, the direct distance between P and R.

Speed

Speed is defined as the rate of change of distance or distance moved per second. It is a scalar quantity. If speed does not vary (if it is constant or uniform) then

Distance is measured in metres per second 

Velocity

Velocity is defined as the rate of change of displacement or displacement per second. It is a vector quantity. If velocity is constant then

The unit of velocity is metre per second

For velocity to be constant, both the speed and direction must be constant.

Acceleration

Acceleration is defined as the rate of change of velocity i.e. the change of velocity per second. If acceleration is constant then

The unit of acceleration is metres per second squared

Acceleration is a vector quantity.

Representation motion using graphs

We use graphs to represent and analyse motion. The most useful to us are graphs of displacement against time, and velocity against time.

Constant Velocity

Ia a car is moving at a constant velocity of 

then every second it will travel a distance of 15 metres in the same direction.

Two graphs can represent this motion:

Displacement/time graph

The graph below represents the car's motion., The gradient of the line is 60/4 = 15. The gradient of a displacement/time graph always represents the velocity.

Velocity/time graph

The gradient of the graph represents the acceleration. In the example below the velocity constant, so the gradient and acceleration are zero.

The area under a velocity/time graph represents the distance travelled. So in 4 seconds, are = 15 x 4 = 60 and the distance travelled is 60m.

Velocity/time graphs are more useful than distance/time graphs. All four quantities are represented on a velocity/time graph: velocity, time, distance and acceleration.

Uniform Acceleration

If a car starts from rest and has an acceleration of 5ms^-2 each second its velocity increases by 5ms^-1

We can represent this in a velocity/time graph as shown below.

We can use the graph to calculate the distance travelled in 6 seconds. Remember that the distance travelled is represented by the are under the graph. The triangle has an area of

The distance travelled in 6 seconds is 90m.

Results for Lab #9

The results for lab #9 are as follows:

Good luck with the SBA :)

Specific Latent Heat of Ice (SBA #8)

Note: When doing labs, it helps to review the topic before doing the questions.

For this lab, you are required to find the specific latent heat of ice using the method of mixtures. Therefore, you need all of the following information:

• The mass of ice used m_i
• The mass of water used m_w
• Initial temperature of water (temperature after heating up the water) θ₁ 
• Final temperature of water (temperature after ice was completely melted) θ₂
• Specific heat capacity of water (4200 J kg^-1 K^-1)

In this experiment, it is assumed that the total energy lost by the heated water was transferred to, or gained by the ice. This implies that:

Total energy lost by water = Total energy gained by ice

Energy needed to change the temperature of a substance is found by the following formula:

The ice gained energy from the water and was changed to a liquid. This change from ice to water is called a change of state. Therefore the energy needed for a change of state from ice to liquid is found by the following equation:

Since the energy lost by the water is equal to the energy gained by the ice then

In words:

the mass of water X specific heat capacity of water X temperature change = mass of ice X latent heat of ice

You can then rearrange the formula to find the specific latent heat of fusion of ice. Hope this helps you.

Good luck!!! :)