Science Forces Studying PDF

Science Forces Studying Defining Force: What is a force? – A force is a push, a pull or a twist – A force can change the speed, direction or shape of an object - e.g. when a racquet strikes a tennis ball, it can cause the ball to change speed and direction; it can also temporari...

Science Forces Studying Defining Force: What is a force? – A force is a push, a pull or a twist – A force can change the speed, direction or shape of an object - e.g. when a racquet strikes a tennis ball, it can cause the ball to change speed and direction; it can also temporarily change the shape of the ball too – Forces act everywhere at all times - they can cause changes to occur - the effects can be obvious or not – For every action (force) there is an equal and opposite reaction – Forces can be classified as either a contact force or a non-contact force – Forces can start an object moving, change its speed, direction or shape – Whenever there is an interaction between 2 objects, there is a force on each of the objects – The bigger the push/pull the bigger the force – The greater the mass of an object, the more force is needed to accelerate or move it Drawing Forces: – Forces are drawn using arrows – The length of the arrow represents the size of the force – The direction the arrow points to is the direction the object is moving – If multiple forces are acting on an object, all of them must be drawn Types of Forces: CONTACT FORCES NON-CONTACT FORCES (2 objects are physically in (2 interacting objects are not in contact with each other) physical contact with each other, yet can exert a push/pull despite their physical separation) Frictional forces, tensional forces Gravitational forces, electrical (created in a string or cable when forces, nuclear force, magnetic pulled tight), normal forces (e.g. forces when you lean against a wall, the wall exerts a normal force on you), air resistance force, buoyancy, surface tension, lift force, drag force, applied forces  – Thrust (is the force generated by a mechanical advantage. e.g. car engine, air plane motor, legs on a bike) – Air resistance = Drag force (the force exerted by ‘air particles’ of an object) – Weight force (created by gravity) – Normal force = Reaction force (action force/reaction force) – Lift force (an upward force that acts on an object moving through air, or a liquid like water. e.g. it allows airplanes to fly (it pushes it upwards)) Measuring Forces: – Force is measured in Newtons (N) - the standard unit for force – A spring balance is a device used to measure forces – SPRING BALANCE: ring (on top to hold it), pointer (clearly indicates how many newtons), graduated/calibrated scale (1N = 100g), hook (used to hold the item that is being measured) Balanced/Unbalanced Forces: – When forces are balanced, the object is stationary – When forces are unbalanced, the object moves, mainly in the direction of the bigger force Net Force: – To calculate the Net Force of an object, you must find the sum of all forces - e.g. 70N < ⸻—[]⸺> 30N – So, +70N + (-30N) = 70N - 30N = 40N to the Left Friction: – Friction is a force that opposes the movement of an object – It occurs between any surfaces that are in contact and sliding past each other – Objects travelling through air/water also experience friction – Friction forces are higher if the surfaces in contact with each other are rough – Small bumps on the surface of a rough object catch on bumps on the surface of the other object and slow down the movement – Friction can act between any 2 materials in contact with each other – When the 2 materials are solids, the force is generally called friction; air resistance occurs when objects are moving through air; fluid friction occurs when objects are moving through liquids – Air resistance or fluid friction are examples of/other names for drag force – Friction can be useful in some cases, while in others they are not (useful: writing/drawing, walking, generating heat by rubbing hands together) (not useful: wearing of machine parts over time, wears out soles of shoes, slows things down) – Friction can be reduced through the use of wheels or lubricants (oil or grease). Polishing/ waxing makes surfaces smoother by removing some bumps or filling up some of roughness  – Air resistance is a powerful example of friction - e.g. as an object, such as a bike, moves through air, a frictional force called air resistance slows movement – Air resistance acts in the opposite direction to the way an object is moving. The faster it moves, the greater the resistance. Air resistance wastes energy, because the resistance must be overcome to move forward Magnetism (Non-Contact Force): – Magnetism is a non-contact force that acts at a distance between objects – Magnets are a special class of objects that generate magnetic forces – This means they can push or pull on other magnets/magnetic materials – Magnetic materials are special materials that can be attracted by magnetic forces but do not generate their own magnetic forces - e.g. nails can be attracted to a magnet, but they are not attracted to each other – Common magnetic materials are: iron, nickel, and cobalt – MAGNETIC POLES: magnets always have a north and South Pole, even if broken in half. Like poles repel, and unlike poles attract (North and North repel, South and South repel, North and South attract) – MAGNETIC FIELDS: the metallic objects attracted to a magnet lie within the magnet’s magnetic field. The magnetic field is the area around a magnet where it’s magnetic force acts. Although magnetic fields are invisible, we can visualise what they look like by sprinkling iron filings around a magnet. The iron filings line up along the magnetic field lines (as seen in image 1). Image 2 shows a drawing of the magnetic field. The lines show the direction of the magnetic force. The lines are closest together where the magnetic force is greatest, and are further apart where the magnetic force is weakest. – INTERACTING MAGNETIC FIELDS LINES: if the magnetic fields of 2 magnets are pointing in the same direction, the fields will add together. This means that the magnetic force will be stronger. In image 1, the magnetic flux lines come out of one magnet’s North Pole and go into the other magnet’s South Pole. This creates a very strong magnetic force between the 2 magnets so they are attracted to each other. If the fields point in opposite directions, they will cancel out. This will make the magnetic force weaker. In the diagrams in image 2, the magnetic flux lines are either both flowing inwards or both flowing outwards. This  causes the magnetic fields to interact in such a way that the magnets are repelled. – There is a particular unit that is used to measure the strength of a magnetic field. Magnetic fields have the symbol B. They are measured in teslas (T). A typical refrigerator magnet has a magnetic field strength of around 5 mT (milliteslas). A millitesla is 1000 times weaker than a tesla. Mainly deal with magnetic fields that can be measured in milliteslas (mT) or microteslas (µT). – ELECTROMAGNETS: a magnet’s pulling force can be very useful, but sometimes it gets in the way. An electro magnet is a magnet that can be turned on and off with the flick of a switch. It is made up of a coil of wire wrapped around a piece of iron. The piece of iron turns into a magnet when electricity passes through the coil. The iron stops being magnetic as soon as the electricity is turned off. – MAGNETIC LEVITATION: if a bar magnet is placed on a bench standing North face up, and a second bar magnet is placed above the first magnet, North end down, what will occur assuming that the second magnet can not fall off the first? - the second magnet will be floating on top of the second magnet. They cannot touch so they must be at a distance from each other. Magnetic levitation is a method where an object is suspended in the air using only magnetic force counteracts (when 2 magnets repel). This is applied to train travel to allow the train to levitate several inches over a track or guideway. This system of transportation is called maglev. Advantages: reduced friction, high speeds, lower  maintenance costs. Disadvantages: expensive, energy consumption, cannot be integrated into existing railroads - require specific, special structures Electrostatics (Non-Contact Force): – Atomic Structure Review: at the centre of each atom is a heavy nucleus. Surrounding the nucleus is a lot of empty space and tiny particles called electrons. Electrons are constantly moving around the nucleus. Each electron carries a negative electric charge. Inside the nucleus are 2 different types of particles. The protons inside the nucleus are much heavier than electrons. Each proton carries a positive electric charge. The neutrons inside the nucleus are similar to protons but carry no electric charge. The positive electric charge of a proton exactly balanced the negative charge of an electron. Atoms usually contain an equal number of electrons and protons. Any material that has more protons than electrons is said to be positively charged. Any material that has more electrons than protons is said to be negatively charged. – Getting Charged: objects usually become charged by the addition or removal of electrons. This charge is called an electrostatic charge because once an object gains an electric charge, it remains ‘static’ or stationary on that object. Only in conductors (mainly metals) do charges move through the object, creating a ‘current’ of charge rather then a static charge. There are 2 ways that an object can gain an electrostatic charge: by friction or by contact with another object that is already charged. – ELECTROSTATICS: there are 2 types of charges, these being positive charge and negative charge. Objects that are charged the same repel each other when brought close together. Objects that are charged oppositely attract each other when brought close together. – Charge on 1st and 2nd objects:  a) 1st: Positive 2nd: Positive b) 1st: Positive 2nd: Negative c) 1st: Negative 2nd: Negative d) 1st: Negative 2nd: Positive Attract or Repel? a) Repel b) Attract c) Repel d) Attract A positively or negatively charged object will charge an uncharged object. All substances are made up of tiny particles called atoms. Atoms have a nucleus of protons which have a positive charge. Orbiting around the nucleus are electrons which have a negative charge. A normal atom is electrically neutral, because it has an equal number of positive charges and electric charges. If some electrons are removed from an atom, it becomes positively charged. If some electrons are added to an atom, it becomes negatively charged. Rubbing substances together can result in the transfer of negative charged particles called electrons. If an object has more electrons than protons, it is negatively charged. If an object has more protons than electrons, then it is positively charged. The charge on each material below is: a) Positive b) Negative c) Neutral d) Negative – When a neutral PVC pipe is rubbed with a neutral rag, they are both charged by friction, making the electrons on the rag move to the pipe, which then makes the rag positive, and the PVC pipe negative (Possible questions: Describe the electrostatic status of an object.  Draw an image of an object that is: a) neutral b) positively charged c) negatively charged) – 2 positively charged ions repel each other – A positively charged ion and a negatively charged electron attract each other Gravity (Non-Contact Force): – Gravity is a non-contact force that attracts objects with mass towards each other – The Earth’s gravity pulls objects down towards the planet’s surface – In the absence of Earth’s gravity, such as in space, objects experience weightlessness – Gravity is the force that ensures that what goes up must come down. It pulls us down towards the Earth, pressing our feet onto the ground, which results in the friction that gives us traction (grip). Gravitational forces are present throughout the universe, holding the moon in orbit around the Earth, and the Earth in orbit around the Sun. It is a force that acts between any pair of objects, whether they are in contact or not. Gravity is therefore an example of a non-contact force. – WEIGHT VS MASS: mass and weight are 2 different things. Mass measures how much matter a substance contains. Mass is how much matter (the number of atoms) an object contains. Regardless of where you are on the Earth, moon, or mars, your mass does not change. Mass is usually measured in kilograms (kg), although other units such as tonnes and grams are often used. Weight on the other hand, is a measure of the size of the gravitational force acting on you. Weight is a force so, like other forces, it is measured in newtons (N). Objects of greater mass have a greater weight. For example, a student with a mass of 60kg has a weight of almost 600N, while a student of mass 50kg has a weight close to 500N. Weight is calculated using the formula: w = m x g (weight = massxgravity). w = weight, m = mass (kg), g = gravity (m/s^2). On Earth, gravity = approximately 9.8N (or 10N rounded). Wherever you go in the universe, your mass is always the same, but your weight depends on the size of the gravitational force acting on you. This gravitational force depends on: a) the mass of the object pulling on you. Your weight on Earth is greater than it would be on the moon because the Earth is so much larger than the moon. b) how close you are to the object pulling on you. The weight of an astronaut for example decreases with increasing altitude. To Do: Go over notes + understand Use topic outline Flash cards PHET Simulations EP + copy Worksheets Slides for practice Cheat sheet Practice test