1. Science 7: Unit D
Structures & Forces

2. Structures & Forces 3: Mass & Forces 1: Types of Structures
2: Describing Structures
4: Forces, Loads & Stresses
5: How Structures Fail
6: Designing with Forces
7: Stable Structures

3. Mass & Force
Topic 3

4. Mass & Weight What is the difference between mass and weight?
Does an elephant weigh the same on the moon as on earth?
Is there less elephant, just because he is on the moon?

5. Mass & Weight

6. Mass & Weight Mass is the total matter in an object
Weight is the force of gravity on an object
The mass of an elephant on the moon is the same as if he is on earth
There is less gravity on the moon, so he has less weight
If he were on Jupiter, his mass would still be the same but his weight would be way higher! (and he might look like a pancake)
Other Planets

7. Mass Mass is the total amount of matter in an object
Units of mass follow the Primary Standard of Mass, the kilogram
Primary Standard

8. Mass Mass is measured using a triple beam balance
The object is put on the balance and mass is added until it is balanced out.
Why is a balance effective for showing mass?

9. Gravity

10. Weight All objects with mass have Gravity
Sir Isaac Newton was the first to describe gravity
The amount of matter in objects and the distance between objects determines the amount of gravity

11. Weight
Weight is determined by the amount of gravity acting on an object
A Newton (N) is the unit of force – including the downward pull of gravity
Weight can be measured with spring scales or force meters in Newtons.

12. Calculating Weight from Mass *** Separate sheet of paper***
Question: If a person has a mass of 50kg what is their weight on earth? Weight (F) = mass(m) x gravity(g) Mass (m) = 50kg Gravity(g) = 9.8 m/s2 F = m x g F = 50 x 9.8 F = 490 Newtons * Notice weight is almost 10x the mass!

13. Weight

14. Triple Beam Balances & Force Meters
Use the scales to measure the
mass (triple beam balance) and
weight (Newton spring scale)
of three different objects
Object
Mass
Weight
Pen
Agenda
Pencil Case (light)

15. Forces Forces are pushes or pulls acting on objects
Force diagrams are a simple way of showing the forces on an object
Direction of force must always be shown

16. Types of Structures
Topic 2

17. Types of Structures
Structures are things with a definite shape and size, serving a particular function
To perform a function a structure must resist forces
Such as pushes or pulls
These forces may change the shape or size
Brick walls resist wind, the bottom bricks support the top ones
If a person climbs the wall it must support the load of the person as well.

18. Types of Structures Natural structures Manufactured Structures
Not made by people
May be biotic or abiotic
Spider webs, mushrooms, feathers, skeletons, caves, mountains
Manufactured Structures
Manmade
Often based on nature
Fishing nets, buildings, roads, walls, beads, umbrellas

19. Types of Structures - Mass
A mass structure is made of similar materials piled together
Snow sculptures, beaver dams, pyramids, mountains, brick walls, cakes & sidewalks
What are some natural and manufactured mass structures?

20. Types of Structures - Mass
Mass structures use a lot of materials
The weight of the materials makes the structure stable
Small spots of wear or breaking seldom make a difference overall - Hadrian's Wall
Not all mass structures are completely solid

21. Types of Structures - Mass
Mass structures must be very carefully designed because of size and weight
Mass structures may fail because:
It may not be heavy enough to stay in place
It is too thin, or poorly fastened and parts may push out of place
It may be so heavy it sinks or leans
It may not be attached to the ground well enough
Baldwin Hills Dam
Better sand bags

22. Think about it!
Bricks are often staggered, this pattern is called a running bond
What might be an advantage of stacking bricks this way?

23. Types of Structures – Frame
Structures made of a strong skeleton
Ladders, bikes, houses, Eiffel Tower, spider webs, people (bones), umbrellas
Some frames are covered, depending on the function
What are some more natural and manufactured frames structures?

24. Types of Structures – Frame
Frame structures are relatively simple to design and build
Often least expensive designs to build
Eiffel Tower

25. Frame - Cars

26. Types of Structures – Frame
Frame structures often need to be anchored
Complicated designs need to be very exact
Small errors in building a frames structure can cause major damage
Minneapolis Bridge

27. Minneapolis Bridge Collapse

28. Think about it?
Tower cranes are frames structures – what are some advantages they have in their design?
Tower Cranes

29. Tower Cranes in Dubai

30. Types of Structures – Shell
Shell structures are typically thin and hollow
Eggs, igloos, umbrellas, cans, skulls, domes, balloons and canoes
Can you think of some more natural or manufactures shell structures?

31. Types of Structures – Shell
They keep their shape and support loads without a frame or solid mass inside
Some are rigid like egg shells, others are flexible like parachutes
They make great containers
They use minimal building materials
Pantheon Dome

32. Types of Structures – Shell
Tiny weaknesses, like scratches can cause failure
Uneven drying/cooling of building materials may cause weaknesses
Construction is often slower and more difficult than other structures
Spangler Eggs

33. Think about it! Are most designs only one type of structure?
Why do you think so many designs combine structure types?
geodesic domes

34. Combining Design
What types are these structures made up of?

35. Structures mins

36. World’s Tallest Buildings