science 8: unit 2 fluids ch. 9 forces -...
TRANSCRIPT
Science 8: Unit 2 FluidsCh. 9 Forces
Science 8 Unit 2: Fluids
Force: Anything that causes a change in the motion of an objectA push or pull on an object
Science 8 Unit 2: Fluids
Force: Anything that causes a change in the motion of an objectA push or pull on an object
• Forces can be balance or unbalanced
Science 8 Unit 2: Fluids
Balanced forces: • Two or more forces equal in strength• Opposite in direction• Results in no movement
Science 8 Unit 2: Fluids
Unbalanced forces: • Forces are not equal and opposite• Results in movement (change in speed or direction)
Science 8 Unit 2: Fluids
Mass Vs. Weight• To understand the force of gravity we must understand the
difference between mass and weight
Mass: The amount of matter in an object
Weight: The pull or force of gravity acting on an object
Science 8 Unit 2: Fluids
Mass• Stays the same anywhere
in the universe• Measured in kg
Weight• Will change with different
gravities• Measured in Newtons (N)
Science 8 Unit 2: Fluids
Buoyancy: • The upward force exerted on an object in a fluid
Science 8 Unit 2: Fluids
Buoyancy: • The upward force exerted on an object in a fluid
Comparing buoyant force to the force of gravity will tell us whether an object will sink or float
Science 8 Unit 2: Fluids
Archimedes Principle: The buoyant force acting on an object equals the weight of the fluid displaced by the object
Science 8 Unit 2: Fluids
Archimedes Principle: The buoyant force acting on an object equals the weight of the fluid displaced by the object
• A 1 L cube displaces 1 L of water
• Buoyant force = weight of 1L water
Science 8 Unit 2: Fluids
• Cubes are same volume• Displace same amount of water• Same buoyant force
Why do the wood and metal cubes sink further than the sponge?
Science 8 Unit 2: Fluids
• Cubes are same volume• Displace same amount of water• Same buoyant force
Ex. Metal• More dense• Force of gravity is greater
than buoyant force• Sinks
Science 8 Unit 2: Fluids
Basic rule:
If the density of the object is greater than the density of the fluid it will sink
Science 8 Unit 2: Fluids
Read from “How Buoyancy and Density are Related” on page 339 to page 342 and answer the questions below:
1. Do we float more easily in salt water or in fresh water? Why?
2. How do life jackets keep a person floating?
3. How do blimps work?
Science 8 Unit 2: Fluids
Pressure
Pressure is the force acting on a given area.
• The larger the force, the greater the pressure.• The smaller the area, the greater the pressure.
Science 8 Unit 2: Fluids
Calculating pressure :
P(Pressure) = F (force )A (Area)
UnitsThe unit for pressure is Newton/ Metre2 which is called a Pascal (Pa)
FP A
Science 8 Unit 2: Fluids
Examples:Finding Pressure
Force= 10 N Pressure= F = 10N = 2 PaArea= 5 m2 A 5m2
Science 8 Unit 2: Fluids
Examples:Finding Pressure
Force= 10 N Pressure= F = 10N = 2 PaArea= 5 m2 A 5m2
Finding AreaForce = 50 N Area = F = 50N = 10m2
Pressure = 5Pa P 5Pa
Science 8 Unit 2: Fluids
Examples:Finding Pressure
Force= 10 N Pressure= F = 10N = 2 PaArea= 5 m2 A 5m2
Finding AreaForce = 50 N Area = F = 50N = 10m2
Pressure = 5Pa P 5Pa
Finding ForcePressure = 6Pa Force = P x A = 6 Pa x 2m2 = 12NArea = 2m2
Science 8 Unit 2: Fluids
k