Midterm review for Physical Science

General Knowledge

Scientific Method

1. Observation (sometimes not used)
2. Question or Problem
3. Research
4. Hypothesis
5. Conduct the experiment
6. Analyze your data
7. Conclusion
8. Report your results

Observation vs. Inference

• An observation is something that is concrete, a fact.
  • The wall is red.
  • She weighs 120 pounds.
• An inference is an educated guess, it may be true or false, it’s not a concrete fact.
  • The wall would look better if it was painted blue.
  • Judging by how she looks, she must weigh over 200 pounds.

Metric System & Conversion Factors

• Scientists use a system of measurement called International System of Units (SI).
• The units of the metric system are:
  • for length – meter (m)
  • for mass – gram (g)
  • for liquid volume – liter (L)
  • for temperature – Degrees Kelvin (K) or Degrees Celsius (C)
• To find solid volume multiply length, width and height. [(l)(w)(h)]
• To convert metric units we can use the acronym “Killer hippos die by drinking chocolate milk.)
  • Kilo – 10³ (1,000x)
  • Hecto – 10² (100x)
  • Deka – 10¹ (10x)
  • Deci – 10^-1 (1/10) .1
  • Centi – 10^-2 (1/100) .01
  • Milli – 10^-3 (1/1,000) .001

• When converting to a larger unit (going backwards) the 1 goes in the numerator and the multiple goes in the denominator (1/multiple)
• When converting from a larger unit to a smaller one (going forward) it’s the opposite, the 1 goes in the denominator and the multiple in the numerator (multiple/1)
• The unit you want to cancel always goes on the bottom.

Lab Instruments

• In the lab, we may use:
  • the beam balance to find mass (in grams)
  • the spring scale to find weight (in Newtons)
  • the graduated cylinder to find liquid volume (in liters)
  • the metric ruler or the measuring tape to find length (in meters)
  • the thermometer to find temperature (in Degrees Celsius)

Scientific Notation

• Scientific notatin is the way that scientists handle very large or very small numbers.
• If you roll the decimal to the left, the exponent is positive. If you roll it to the right, the exponent is negative.
• The final result must be 1 or more but less than 10.

Chapter 1: Motion

Vocabulary

1. motion – the state in which one object’s distance from another is changing
2. reference point – a place or object used for comparison to determine if an object is in motion, fixed objects make good reference points
3. International System of Units – a system of measurement based on multiples of ten and on established measures of mass, length, and time
4. distance – the length of the path between two points
5. speed – the distance an object travels per unit of time (scalar)
6. average speed – the overall rate of speed at which an object moves; calculated by dividing the total distance an object travels by the total time
7. instantaneous speed – the speed of an object at one instant of time
8. velocity – speed in a given direction (vector)
9. slope – the steepness of a graph line; the ratio of the vertical change (the rise) to the horizontal change (the run)
10. acceleration – the rate at which velocity changes (vector)

Relative Motion

• You may/may not be in motion depending on the reference point you choose.
  • You may be sitting in your chair. If you use your chair as a reference point you’re not moving. If you use the Sun as a reference point you’re moving because Earth is moving around the sun.

Graphing Motion

• You can show the motion of an object on a line graph in which you plot distance versus time.
• On a distance versus time graph:
  • time is plotted on the x axis (horizontal)
  • distance is plotted on the y axis (vertical)
• On a speed versus time graph:
  • time is plotted in the x axis (horizontal)
  • speed is ploted in the y axis (vertical)

Acceleration

• Acceleration is a vector quantity.
• A change in direction, in speed, or in both is acceleration.
• Negative acceleration (decreasing speed) is called deceleration.

Chapter 2: Forces

Vocabulary

1. force – A push or pull exerted on an object.
2. newton – A unit of measure that equals the force required to accelerate 1 kilogram of mass at 1 meter per second per second.
3. net force – The overall force of an object when all the individual forces acting on it are added together.

4. friction – The force that two surfaces exert on each other when they rub against each other.
5. sliding friction – Friction that occurs when one solid surface slides over another.
6. static friction – Friction that acts between objects that are not moving.
7. fluid friction – Friction that occurs as an object moves through a fluid.
8. rolling friction – Friction that occurs when an object rolls over a surface.
9. gravity – The attractive force between objects; the force that moves objects downhill.
10. mass – The amount of matter in an object.
11. weight – A measure of the force of gravity acting on an object.

12. inertia – The tendency of an object to resist a change in motion, it depends on mass.

13. momentum – The product of an object’s mass and velocity.
14. law of conservation of momentum – The rule that in the absence of outside forces the total momentum of objects that interact does not change.

15. free fall – The motion of a falling object when the only force acting on it is gravity. (9.8 m/s²)
16. satellite – Any object that orbits around another object in space.
17. centripetal force – A force that causes an object to move in a circle.

Net Force

• The combination of all forces on an object is called net force, that is the force that is actually determines how it will accelerate.
• When forces are acting on opposite sides, subtract them.
  • If an object is being pushed with 10N of force to the left and 20N of force to the right it’ll move with 10N of force to the right.
• If the same force is being put on an object from opposite sides the forces are balanced forces, and have a net force of 0N.
  • If an object is being pushed with 10N of force to the left and 10N of force to the right, its net force is 0N, it won’t move.
• If forces are acting on the same direction, we add them to get the net force.
  • If two people are pushing an object to the left with 10N of force each. the object will move to the left with 20N of force.

Friction

• Friction is the force two surfaces exert on each other when they rub against each other.
• The two factors that affect friction are:
  • types of surfaces
  • how hard the surfaces are pushed together
• Friction acts in a direction opposite to the object’s motion.
• Without friction an object won’t stop moving.
• There are four types of frictions, they are:
  • sliding friction – occurs when two solid surfaces slide over each other, it’s what makes moving objects slow down and stop
    • When a penguin slides down a hill sliding friction makes it slow down and stop, if not it wouldn’t stop until it hit the wall. The friction is uphill if the penguin is going downhill, that’s why we sometimes see snow coming out behind, because of friction.
  • static friction – acts between objects that aren’t moving
    • If you try to push a couch across a room you have to push hard enough at first to overcome static friction, after this there will be sliding friction.
  • fluid friction – occurs when a solid object moves through a fluid, it’s easier to overcome than sliding friction
    • When we swim we undergo fluid friction, that’s why we push water backwards to go forwards; the friction acts in the opposite direction.
  • rolling friction – occurs when an object rolls across a surface, it’s easier to overcome than sliding friction for similar materials
    • When we pedal a bike the wheels are having rolling friction with the ground in the opposite direction we’re going.

Universal Gravitation

• Newton realized that gravity acts everywhere in the universe, that discovery is now called the law of universal gravitation.
• Gravitational force exists between any two objects, however, most forces are very small and depend on mass.  The greater the mass of something the more attraction objects will have towards it.
• Mass is not weight, weight is a measure of the force of gravity of an object. Your mass is always the same no matter where you are, however your weight might be different in the Moon, in Mars, etc.

Newton’s Laws of Motion

• Sir Isaac Newton was an English physicist. He stated 3 laws of motion, which are:
  1. An object at rest will remain at rest unless ated upon by a nonzero net force. An object moving at a constant velocity will continue moving at a constant velocity unless acted upon by a nonzero net force. (Also called the law of inertia)
  2. An object’s acceleration depends on its mass and on the net force acting on it. (acceleration = net force/mass)
  3. If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. (For every action there is an equal but opposite reaction.)
     • The ground pushes forward on your feet with equal and opposite force when you walk.
     • Action-reaction forces don’t cancel each other because they act on different objects.

• The unit used to measure force is called a Newton after Sir Isaac Newton. One newton equals the force it takes to push 1kg for 1m per second. This can be expressed as  N = kg/m/s²