Science 7 Unit D Structures Forces Structures Forces

Science 7: Unit D Structures & Forces

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

Mass & Force Topic 3

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?

Mass & Weight

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

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

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?

Gravity

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

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.

Calculating Weight from Mass *** Separate sheet of paper*** Question: If a person has a mass of 50 kg what is their weight on earth? Weight (F) = mass(m) x gravity(g) Mass (m) = 50 kg Gravity(g) = 9. 8 m/s 2 =mxg F = 50 x 9. 8 F = 490 Newtons * Notice weight is almost 10 x the mass! F

Weight

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 Pen Agenda Pencil Case (light) Mass Weight

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

Types of Structures Topic 2

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.

Types of Structures Natural 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

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?

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

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

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

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?

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

Frame - Cars

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

Minneapolis Bridge Collapse

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

Tower Cranes in Dubai

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?

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

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

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

Combining Design �What types are these structures made up of?

Structures 20+mins

World’s Tallest Buildings