Chapter 2 Density and Flotation:
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The area of a shape is the amount of surface enclosed within its boundaries
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The unit for area is a square meter or a meter squared
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The volume of an object is the amount of space it takes up
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Volume is measured with the unit: Cubic meters or cubic centimeters
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When the top of the water is slightly curved it is known as the meniscus. You must always read the lowest level of the meniscus
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To get the volume of a shape you must multiply length by width by height
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However if you need to measure the volume of an irregular object we used displacemnet
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The mass of an object is the amount of "matter" in it
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The density of a substance is its mass per unit of volume
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To measure mass we multiply density by volume
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To measure volume we multiply mass by density
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To measure density we divide mass by volume
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To remember these three calculations we use a traingle as you can see above.
Terms to Note:
Left: The triangle can be used to help us memorise formula. A possible way of using it is by covering the measurement we want
Right: The method of measuring the volume of irregular shapes such as rocks
Flotation and speed:
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A substance will float in the liquid if the substance is less dense than the liquid
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The speed of an object is the distance it travels per unit of time
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The calculation of average speed is distance travelled divided by time taken to do so
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Distance is calculated by multilpying speed travelled by time taken to do so
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Time is calculated by dividing distance travelled by the speed they travelled at
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Like density, volume and mass we use a similiar triangle known as "d street" to help us remember the differnt formula
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The unit of measurement for speed is kilometers per hour (km/hr) and meters per second (m/s1)
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In the physics section of your exam you will encounter time-distance graphs which you may have to fill in or answer questions on.
A time-distance graph as you will see it in the exam
The "d street" method is similiar to the density, volume and time triangle
Velocity and acceleration:
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The velocity of an object is its speed in a certain direction
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For example a plane could be travelling from Dublin to London at a speed of 700 km/hr but its velocity is 700km/hr south-east
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Acceleration is the rate of change of velocity
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This is calculated by dividing change in velocity by time taken for that change to occur
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The unit of acceleration is the unit of speed/velocity divided by the unit of time
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The unit of measurement of velocity is meter per second per second or meter per second squared. This is written as M/S2
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We also will encounter velocity-time graphs in the exam which is similiar to the distance-time graphs. This tells us how the velocity of an object varies with time
Velocity-Time Graphs
Calculation for acceleration
Difference between mass and weight:
Weight: Mass:
- Weight is a force created by gravity - Mass is measured in grams
- Measured in neutrons - Mass is how much matter something has
-Weight reduces as you rise upwards - Mass is constant