Introduction to Physical Science Monday Wednesday Thursday Tom

Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine tomburbine@astro. umass. edu

Density • Density = Mass/Volume • Mass is usually in grams or kilograms • Volume is usually in cm³ or m³

Densities • Density of water = 1 g/cm³ = 1, 000 kg/m³ • Density of iron = ~8 g/cm³ = ~8, 000 kg/m³

Weight density • Weight density = weight/volume

Pressure • Pressure = Force/Area • Unit of pressure is a Pascal, – which is a newton per square meter

Pressure in a liquid • When you swim, you feel the pressure of the water plus air above you • It is the weight of the fluids (water and air) above you • Swim deeper, more pressure

Pressure in a Liquid • Liquid pressure = weight density x depth

Pressure in a liquid • Liquid pressure is exerted equally in all directions

Buoyant Force • Upward acting force, caused by fluid pressure, that opposes an object's weight

Equal Volumes • Equal volumes feel equal buoyant forces • Cork would float, aluminum would sink, and lead would sink faster • Difference in their behavior is due to their weight

Archimedes (287 BC-212 BC) • Greatest scientist of antiquity • Needed to determine if silver had been substituted for gold in a crown for a king • Mass could easily be determined but not mass • Discovered that you could determine the volume of the crown by submerging it in water • Density (mass/volume) could be determined and compared to pure gold • This story may not be true

Archimedes Principle • An immersed body is buoyed up by a force equal to the weight of the fluid it displaces

Meaning • When an object is immersed in water, it feels lighter • Apparent weight of object is the weight of object minus the buoyant force N N 3 N of

Principle of Flotation • A floating object displaces a weight of fluid equal to its own weight

Why does an iron ship float? • Iron is about eight times as dense as water • When submerged, displaces 1/8 of a ton of water • If the iron is in a bowl and displaces 1 ton of water, it floats

• Buoyant force equals the weight of the fluid it displaces • Denser fluids exert more buoyant force upon a body than less-dense fluids of the same volume • A ship floats higher in salt water than in fresh water because salt water is slightly denser than fresh water so it has higher mass and exerts a higher buoyant force

• http: //www. youtube. com/watch? v=e. Qsmq 3 Hu 9 HA

Any Questions?