8 th grade semester review

1. 8th grade semester review Tests begin Friday for 1&2 A day classes Monday 1&2 Bday, Tuesday 3&4 A day, Wednesday 3&4 B day

2. MOTION

3. Distance Time Graphs • In the distance time graph you just drew, make sure you know/understand that the LINE you see on the graph tells you what the object is doing. • If the line is at a diagonal from the left corner up to the right, the object is accelerating. If it remains straight, it is traveling at a constant velocity. • If the line is straight across at any point, the object is not moving. • If the line is at a downward slope (top left to bottom right), the object is decelerating or slowing down. If it changes direction, it is also accelerating! Remember that!

4. Motion continued • Motion can be described by its direction, speed and position • With motion, the speed of an object can change and the velocity will not. • To find an object’s average speed, take the TOTAL DISTANCE and divide by the TOTAL TIME

5. To Find Velocity • Velocity is speed in a certain direction. • Formula for speed is distance/time • If a car is traveling 20 miles in 60 minutes, what is it’s velocity in mph? to set this up you will divide 20 (inside the division bar) by 60 (outside the division bar)

6. Newton’s Laws • Law one – Also called the Law of Inertia! • An object at rest remains at rest or an object in motion remains in motion at a constant speed unless acted on by an unbalanced force. • Give examples • Remember our powerpoint on the man in car when he hit the barrier – he kept going at the same speed as when he hit the barrier!

7. Law Two • The force of an object depends upon it’s mass times it’s acceleration. As something accelerates, the force will increase. • Remember, all things fall at a rate of 9.8m/s/s, except those things that catch air resistance. • Know what types of surfaces have great amounts of friction and those that have least amount of friction

8. Newton’s 3rd Law • For every action there is an equal and opposite reaction; • Examples: * Riding a skateboard – pushing off towards the back and the skateboard propels forward. * a rocket taking off – fuel projects force downward and the rocket launches upward

9. Law of Conservation of Mass • Matter is neither gained nor lost in a chemical reaction. • In a reaction, if 3 grams of something is produced, then that means 3 grams of that substance was consumed.

10. pH levels • 0-6.9 is an acid • 7.1-14 is a base • 7 is neutral • A natural environment would be around 7 so if something were living in an environment and the pH level of the water changed drastically, then the organism would die off

11. Qualitative and Quantitative Data • Quantitative data will always involve numbers (150g, 200 mL) • Qualitative data will involve descriptions (adjectives) (blue, wet, slippery)

12. Experiments • When designing experiments, you should always design with a control (ONE) and use a large sample size. • In a controlled experiment, one variable is fixed while all others are changed. • For example: If you were testing if the class enjoys peanut butter sandwiches over ham sandwiches, you shouldn’t conclude that everyone prefers peanut butter just because a few do – test the whole class.

13. Electromagnetic Spectrum • Wavelengths – • Remember that the higher the frequency, the shorter and more frequent the waves will be • The Lower the frequency, the wider and less frequent the waves would be. • High frequency means high energy • Low frequency means low energy • Plants benefit most from UV light during photosynthesis

14. Electromagnetic specturm • Waves in order of lowest to highest • Radio, microwave, infrared, visible light, ultraviolet, xray, gamma • Remember this sentence: • Real monsters invade vacant universal xylophone games

15. Periodic Table • It is the PROTONS that distinguish one atom of an element from another. • Metals are • Malleable – can be pounded into thin sheets • Ductile – can be drawn into thin wires • Conductive – can conduct heat and electricity • Alkali Metals are the most reactive • Finding Neutrons – subtract the bottom number from the top number in the element’s box. Example – Carbon’s atomic number is 6 and it’s mass is 12. 12-6 = 6; carbon has 6 neutrons.

16. Parts of an atom • Know, in an atom, where the following are located: • Protons, neutrons, electrons • Know the difference (compare and contrast) between a Bohr’s model (shows all of an elements electrons) and a Lewis structure (shows just the valence electrons) • Knowing the number of protons an element has should help you know what type of element it is – metal, nonmetal or metalloid

17. Types of Reactions • Synthesis – A + B --- AB • Decomposition - AB --- A + B • Replacement - A + BC -- AB + C or AB + CD - AC+BD • The first one is single replacement – the second is double • Make sure you can pick out an equation that is balanced. Each of the elements must have equal parts on both sides of the arrow.

18. Reactions • Endothermic reactions – • Endothermic - a process or reaction that absorbs energy in the form of heat. • Breaking a chemical bond requires energy and therefore is Endothermic. • Endothermic reactions usually feel cold because it is taking heat away from you. • Example – making ice cubes

19. REACTIONS (cont.) • Exothermic - example – melting ice cubes; the word describes a process that releases energy in the form of heat. • Forming a chemical bond  releases energy and therefore is an exothermic process. • Exothermic reactions usually feel hot because it is giving heat to you

20. Valence Electrons • These are electrons in the outer ring of the electron shell of a Bohr’s Model. A Bohr’s model shows all of an elements electrons. • Shell 1 – holds no more than 2 electrons • Shell 2 – holds no more than 8 electrons • Shell 3 – holds no more than 8 electrons • Shell 4 – holds no more than 18 electrons • Shell 5 – holds no more than 32 electrons

21. Valence Electrons and bonding • Elements in families 1-4 will tend to lose electrons in bonding. • Elements in families 13-17 will tend to gain the electrons in bonding • Families 3-12 vary (it depends) • Covalent bonding is bonding between two non metals • Ionic bonding is bonding between a metal and a non metal

22. BONDING • All elements in a Period (row across) on the PTE have the same number of energy rings (shells) • All elements in a family (column going down) have the same number of valence electrons. Ex: Family 1 has 1 valence electron. • Family 1 will bond best with family 17 b/c their valence electrons make the happy number 8

23. Frame of Reference • With moving objects, you have what is called a frame of reference. That is, An object may appear to have one motion to one observer and a different motion to a second observer, depending on how the two observers are moving with respect to one another. • Example: if someone is in a moving car and they want to know how fast the car is moving in relation to the ground, the best point of reference would be something standing still on the side of the road (a tree).