Please complete Part 1, 2 and the Analyze question of pg .313. You do not have to do part 3 and 4.
If you do not have a marshmallow that is okay! You can use an old sponge - or anything that would compress the same way. Otherwise try and imagine to the best of your ability what would happen to the grid.
Start Part 1 by drawing a grid onto your marshmallow and then exert the actions listed in the chart. Show what happens to the grid and describe the grid changes and the type of forces observed.
For Part 2: Take a scrap piece of paper and tear it, cut it with sharp scissors and then with dull scissors - draw your observations and then describe it in words for each .
push or pull that tends to cause an object to change its movement or shape The actual effect of a force relies on these three things:
Magnitude (amount of the force)
Direction (where the force is going)
Location (where the force is applied)
Force meter = or spring scale, a common laboratory instrument for measuring forces. Some forces are very large or otherwise difficult to measure.
To completely describe a force, you need to determine both its direction and its size.
Newton
Unit of Force is referred to as a NEWTON (N) 1 Newton (N) = amount of force needed to hold up a mass of 100 grams (g) E.g.) 1 N is a small force, just enough to stretch a thin rubber band 10 N lifts one L carton of milk 200 N force of a hard thrown baseball hitting your hand 1 kg mass is about 10 N (9.8N to be exact)
External Force
Force which is applied on a structure by something else
Walking into the ocean and waves hit your body
The Earth's gravity is a force that pulls towards the center of Earth, therefore Gravity is an External Force
Mass
The mass of an object is the measurement of the amount of matter in the object.
Greater the Mass = Greater the Gravitational Force on that object (it's heavier)
Mass is generally measured in grams or kilograms
Weight is actually the pull of gravity on a mass.
We use a balance to measure mass (kg, g or mg)
Mass is CONSTANT - Does not change no matter where you are
Only changes if you add or take away matter
Mass and Force
Gravity: Is a force
Gravitational force is dependent on:
The mass of the two objects – the greater the force
The distance between the two objects – the closer together the greater the force.
Earths mass is so much greater than anything on it that it’sgravitational force dominates
The force of earths gravity changes depending on where you are in relation to its core – mountain top, space
Weight
Is a measure of the force of gravity exerted on a mass (scientific definition)
Weight is NOT a constant
It changes depending on where you are because gravity changes depending on where you are because gravity changes depending on where you are
You weigh more on Jupiter because its mass and therefore its gravity is greater
You will weight slightly less on top of a mountain and in a plane
You would be weightless in outer space and when you are away from the pull of earth
Bill Nye: Structures
Force Diagrams
A drawing that uses arrows to represent the direction and strength of one or more forces.
The arrow, in a force diagram, is usually drawn pointing away from the place where the force is acting.
Mathematicians are able to use scale drawings and calculations to predict what will happen when many forces are acting on a given object.
Stable Structures
A stable structure is one that is not likely to tip or fall over. It is important that home builders understand the properties of the ground they are building on. If they do not, then the houses that they are building can be damaged by the shifting soil.
Spin Stabilization
Spin Stabilization – the tendency of an object that is spinning on its axis to move in a predictable manner
ex. The faster a bicycle wheel spins the more stable it is.
Centre of Gravity
An imaginary point in any structure where the downward force of gravity acts. Location of the Centre of Gravity will determine the stability of a structure.
1. EVERYONE STAND UP AND FIND A PLACE IN THE ROOM 2. HOLD YOUR ARMS OUT STRAIGHT FOR 2 MINUTES, WHAT IS HAPPENING? 3. STAND ON ONE FOOT AND TRY TO KEEP BALANCE, WHAT ARE YOU EXPERIENCING?
ANSWER - GRAVITY! IS HAVING AN EFFECT ON YOUR STABILITY
Symmetry
Balanced ratio of mass which occurs on both sides of a line/plane or around the centre of the axis The force of gravity on either side of the center point is equal
For a symmetrical structure to be stable, the mass of that structure must be distributed equally around the centre of the structure’s base, meaning force of gravity around the centre is also equal
How Structures Fail
If a great enough force is applied to a structure, it will begin to fail.
Levers create large forces – a lever is a device that can change the amount of force needed to move an object (e.g. with a crowbar, you can lift very heavy objects. Some levers consist of a long arm that rests on a pivot or fulcrum)
Materials Fail: external forces can cause internal forces in the structure. These internal forces can cause damage.
Internal Forces
Forces that act within a structure
One part of a structure exerts on other parts of the same structure
Three Types of Internal Forces
1. Compression 2. Tension 3. Shear
Compression
A force that acts on an object or push parts together within an object
Tension
A force that acts to stretch and pull apart something
Shear
A force which push parts which are in contact with each other in opposite directions
Complementary Forces
When different kinds of internal forces act on a structure at the same time Example: Bending
Compression is put forth on the top and tension is put forth on the bottom
Failure to resist either results in the beam breaking
Static and Dynamic Loads
When structures are built the idea of having weight put on them is something every engineer or designer must think about.
LOAD: External force on a structure
Two Types of Loads 1. STATIC
Weight of a structure and the non-moving load it supports
Example: books on a bookshelf
2. DYNAMIC
External force that moves or changes with time
Example: moving students on a staircase at school
Note: When you build a dynamic structure you must consider you may have both static and dynamic loads, therefore the structure must maintain both