7K and 7J - Test 2 PDF
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This document contains notes on different types of forces, including contact and non-contact forces, and their applications. It also covers concepts such as mass, weight, springs, and series and parallel circuits. The document includes definitions, explanations, and questions relating to the concepts.
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7K – DIFFERENT P. 168-169 FORCES DEFINITION OF A FORCE A force is a push or a pull. Forces can change the shape of something, its speed, or the direction that it is moving in. A force has both magnitude and direction, making it a vector quantity. Objects interact (affect each other) by...
7K – DIFFERENT P. 168-169 FORCES DEFINITION OF A FORCE A force is a push or a pull. Forces can change the shape of something, its speed, or the direction that it is moving in. A force has both magnitude and direction, making it a vector quantity. Objects interact (affect each other) by exerting forces on each other. CONTACT FORCES: IF THE OBJECTS ARE TOUCHING Examples of Contact forces 1.Normal Force 2.Friction 3.Tension 4.Air resistance 5.Drag 6.Upthrust NON-CONTACT FORCES: OBJECTS ARE NOT TOUCHING Examples of Non-Contact forces 1. Gravitational Force 2. Electrostatic Forces 3. Magnetic Forces Both MAGNITUDE and DIRECTION are required Forces are measured in Newtons (N). One newton is equal to the amount of force needed to accelerate a 1 kg mass 1 m/sec2. In other words, a kilogram mass exerts about 9.8 newtons of force. 1. make it change speed, direction or shape 2. a. three of: friction, air resistance, water resistance, upthrust b. Force gravity, magnetic force, electrostatic force 3. The newton (N) 4. a. the motorbike b. It has a bigger force arrow. c. They will start to move/speed up; the motorbike will accelerate/speed up faster than the bicycle WHAT ARE MASS AND WEIGHT? Mass is the amount of matter in an object and is measured in kilograms (kg). Mass is not a force. An object, such as this satellite, has the same mass at any point in the Universe (i.e. mass is constant everywhere). Weight is a force and is caused by the pull of gravity acting on a mass. Weight is measured in newtons(N) and has both magnitude and direction. An object’s weight changes depending on where it is in the Universe. MASS AND WEIGHT Your weight is the force of gravity pulling on you. Weight is a force so its units are newtons (N). If you talk about something being 110 kilograms' you are talking about its mass. Mass is the amount of matter that makes up (N) an object. The units for measuring mass are grams (g) and kilograms (kg). 5 a the force of gravity pulling on something b newtons (N) c the amount of matter in something d kilograms (or grams) (kg or g) SO, WHICH ONE STAYS THE SAME AND WHICH ONE CHANGES? 6. Gravity is not as strong on the Moon as it is on the Earth. 7. so that they all mean the same thing when they talk about a kilogram; this would be important in replicating experiments (accept similar explanations) CALCULATING THE WEIGHT ON EARTH – EXAMPLES Mass (Kg) Weight (N) 50 600 0.7 2.5 36.7 7KB – SPRINGS P. 168-169 SPRINGS Materials and objects can be stretched (made longer) or compressed (made shorter). The amount of stretch or compression in the material depends on the type of material and the size of the force. It takes a very big force to change the size of some materials. Most springs are made from coils of wire. EXTENSION OF A SPRING The extension of a spring is the difference between its original length and its stretched length. The spring is elastic because it will return to its original length when the force is removed. FORCE AND EXTENSION: HOOKE’S LAW Graph D shows that the extension is proportional to the force up to a certain point, called the limit of proportionality. This means that for every 1 N increase in the force, the spring stretches by the same amount. The idea that the extension is proportional to the force is Hooke's Law. Hooke's Law does not apply to all elastic materials. If enough force is applied to a spring, it will pass its elastic limit. The spring will then no longer return to its original length. Materials that do not return to their original shape when a force is removed are plastic materials. a. A b. A and C; the graphs are straight lines/the extension is proportional to the force c. A as it stretches the most for a small weight. This would make the scale easier to read/make it possible to detect small differences in force. FRICTION Friction is the force between two touching objects. It can slow things down or make things stay still. The friction between your clothes and a chair stops you from sliding off the chair. Walking would be very difficult without the friction between your feet and the floor - you would slip and slide everywhere. We can increase friction by using certain materials. For example, rubber produces a lot of friction. The rubber tyres of a Formula One racing car stop the car from sliding off the road as it speeds round sharp bends. Friction is not always useful. Sometimes we want things to move easily. For example, a bicycle is very difficult to ride if there is too much friction in the axles. We can reduce friction by making surfaces smooth or by using lubricants such as oil or grease. Adding a lubricant is called lubrication. Chapter 7J Current Electricity Pages: 152-165 American Academy Larnaca Science Department Background information Everything is made of atoms / particles. Particles have certain properties, e.g. certain mass and electric charge. Electrically charged particles can either be positive or negative. Most bodies around us are not charged i.e. they are neutral. Neutral bodies possess an equal amount of positive and negative particles. Background information In the case that charged particles can flow through a material, then, electricity flows through the material. Chapter 7Jb Models for circuits Pages: 156-157 Chapter 7Jb: Models for circuits Some materials allow charges to move easily around them. We call those materials conductors. A conductor is a material which allows charges to move easily through it. On the other hand, some other materials do not allow charges to move around that easily. We call those materials insulators. An insulator is a material which does NOT allow charges to move easily through it. Chapter 7Jb: Models for circuits Chapter 7Ja Switches and current Pages: 152-153 Chapter 7Ja: Switches and current Current Current = how much charge flows through a certain point of a wire over a certain period of time. In other words, If a lot of charge passes through a wire, in a short period of time current is high. If a small amount of charge passes through a wire, in a long period of time current is low. Chapter 7Ja: Switches and current Components of a circuit Chapter 7Ja: Switches and current Questions 1 how much charge flows through a certain point of a wire over a certain period of time. Chapter 7Ja: Switches and current Drawing electrical circuits Scientists do not draw circuits as they look in real life. This is because it takes too long and each person would draw something slightly different. Instead, they use circuit symbols to represent each component in the circuit. They are drawn exactly the same way each time! Wires are drawn as straight lines. o They do not have to represent the real lengths of the wires. Chapter 7Ja: Switches and current Basic list of symbols Component Symbol Bulb Open switch Closed switch Cell Battery Resistor Variable resistor Ammeter Voltmeter Motor M Chapter 7Ja: Switches and current Current and circuits For current to flow in a circuit, you need: 1. a complete circuit with no gaps. 2. a cell or power supply – provides the energy to the charges, making them move. Chapter 7Ja: Switches and current Current and circuits The bulb will only light if there is a battery and a complete circuit. Chapter 7Ja: Switches and current Filaments in bulbs Bulbs light up because the electricity flowing through them makes the filament glow. If you add more bulbs to the circuit, all the bulbs of the circuit will be dimmer. Chapter 7Ja: Switches and current Switches A switch can open or close a circuit, to either stop or allow the flow of current. When you close the switch you turn on the lights. When you open the switch you turn off the lights. Chapter 7Ja: Switches and current Switches An open circuit does not have a complete path so no current flows. A closed circuit has a complete path, allowing current to flow. Chapter 7Ja: Switches and current What happens when we add more bulbs to a circuit? They all get dimmer! Why? Two ways to be explained: 1. The same charged particles now have to pass through two bulbs, instead of one the energy that the particles carry needs to be divided between the two bulbs. 2. The resistance of the circuit is higher with more bulbs (it is harder for the electricity to get through) – more about resistance in 8Jd. Chapter 7Ja: Switches and current Questions Switch is open: the current cannot flow and the bulb stays off Switch is closed: current can flow and the bulb comes on. Chapter 7Ja: Switches and current Questions The other bulb will not come on because the missing bulb has made a gap in the circuit. Chapter 7Ja: Switches and current Questions Chapter 7Ja: Switches and current Questions Chapter 7Ja: Switches and current Questions Chapter 7Ja: Switches and current Measuring current Current is measured using an ammeter connected in series. The units of measurement for current are amperes, amps (A). The current through each component is the same so it does not matter where we place it in the circuit. Chapter 7Ja: Switches and current Measuring current Chapter 7Ja: Switches and current Questions Chapter 7Ja: Switches and current Questions current ammete cell r filament switch battery Chapter 7Ja: Switches and current Questions Chapter 7Ja: Switches and current Questions batter 0.3 A y Chapter 7Ja: Switches and current Questions cell make the current flow /bulb open gap light close the switch Chapter 7Ja: Switches and current Questions The other bulb will go off, because there is a gap in the circuit. Chapter 7Ja: Switches and current Questions charges metal s insulatin g Chapter 7Jc Series and parallel circuits Pages: 158-159 Chapter 7Jc: Series and parallel circuits Series and parallel circuits Series circuit Parallel circuit A series circuit is a closed circuit A parallel circuit is a closed in which the current follows one circuit which has two or more path. paths for current to flow through. Chapter 7Jc: Series and parallel circuits Series and parallel circuits Chapter 7Jc: Series and parallel circuits Series circuits - Characteristics If one bulb breaks, all the others go off. o This is because the broken bulb creates a gap in the circuit. The current is the same everywhere. If we add more bulbs, the brightness of all bulbs decreases. Chapter 7Jc: Series and parallel circuits Parallel circuits – Characteristics If one bulb breaks, the other bulbs on different branches stay on. The current splits to the different branches. o The sum of the current in the branches is equal to the current in the main part. If we add more bulbs, the brightness of all bulbs stays the same. Chapter 7Jc: Series and parallel circuits Current in series and parallel circuits The current is the same everywhere in a series circuit, but in a parallel circuit the current from the cell splits up when it comes to a branch. The currents in all the branches add up to the current in the main part of the circuit (see circuit C). Chapter 7Jc: Series and parallel circuits Current in parallel circuits If there is an open switch in one of the branches of a parallel circuit, then all of the current goes to the other branch. If there is an open switch in one of the branches of a parallel circuit, then there is no current flowing to that specific branch. Chapter 7Jc: Series and parallel circuits Brightness of bulbs in series and parallel circuits If you add more bulbs to a series circuit the current gets smaller and the bulbs gets dimmer. In a parallel circuit, if you add more branches with bulbs in, the bulbs stay bright. It is easier for the current to flow with more branches, because there are more ways for the charges to go. The current in the main part of the parallel circuit increases. Chapter 7Jc: Series and parallel circuits Switches in series and parallel circuits A switch in a series circuit controls all the components of the circuit. A switch in the main part of a parallel circuit controls all components in all branches. A switch in a branch of a parallel circuit controls the components of that specific branch. Chapter 7Jc: Series and parallel circuits Summary of series and parallel circuits Series circuit Parallel circuit …the other bulbs on different If one bulb breaks… …the others go off. branches stay on. The current… …is the same everywhere. …splits into the different branches. If you put more bulbs… …all bulbs get dimmer. …they all stay equally bright. Chapter 7Jc: Series and parallel circuits Questions Chapter 7Jc: Series and parallel circuits Questions Chapter 7Jc: Series and parallel circuits Questions Chapter 7Jc: Series and parallel circuits Questions Chapter 7Jc: Series and parallel circuits Questions Chapter 7Jc: Series and parallel circuits Questions Parall Serie el s Chapter 7Jc: Series and parallel circuits Questions if you add more bulbs to a series circuit they get dimmer OR if you add more bulbs to a parallel circuit they stay the same brightness. the current is not the same everywhere in a parallel circuit OR the current is the same everywhere in a series circuit. if you add more bulbs to a series circuit the current gets smaller Chapter 7Jc: Series and parallel circuits Questions Both bulbs are in one loop of wire in the series circuit, whereas in the parallel circuit each bulb is in its own piece of wire (or similar answer). Chapter 7Jc: Series and parallel circuits Questions D C E F C is a parallel circuit so has two branches with bulbs on, whereas D is a series circuit The switch is in a different place. The switch is in a different place. the bottom bulb will be on no bulbs will be on no bulbs will be on no bulbs will be on