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Forces
Emmanuel College Y7
| Term | Definition |
|---|---|
| Forces | A push, a pull or a twist. Occur between two or more objects. These objects can be living or non-living. |
| Gravity As A Force | A force that is pulling you towards the centre of the Earth. |
| Forces When Sitting In A Chair | When you sit on a chair the chair has a force that is pushing against you changing the shape of your leg muscles. The reason why you don't move is because the forces acting you are matched |
| Forces In Kicking A Soccer Ball | When you kick or throw a ball, you use energy to create a push force. This force causes the ball to move. When you catch a ball, you are giving it a push. This time, the push force causes the ball to stop moving. |
| Forces Cause Objects To | Begin to move, speed up, slow down, stop moving, change direction, change shape, spin and remain still |
| Measuring Forces Using A scale | One way to ‘see’ a force at work is to measure it. Chief's use scales to measure how much the Earth’s gravity pulls on the ingredients. Twenty grams of flour is pulled to the centre of the Earth, causing the flour to push down on the scales. |
| Measuring Forces Using A Spring Balence | Forces can be measured using a spring balance/newton metre. A stiff spring in the balance stretches when an object pulls on it. This moves the marker and so the amount of force is measured. A rubber band can measure the size of forces in a similar way, |
| Why does a measuring device need to be calibrated | Before we can use a rubber band to measure a force, it must be calibrated. This means matching the stretch of the rubber band to the force pulling on it. So the measurements are accurate and reliable |
| Unit to measure forces | The unit used to measure forces is called the newton after English physicist Sir Isaac Newton (1642 –1727), who first described the force used to pull an apple from a tree. 100g=1N |
| Standard Measurement Of Newtons | All Scientists agree to one measurement so they can communicate with one another. In every country, the force of 100g being pulled to the centre of the Earth is about 1 newton (N). This is about the same as one large chocolate bar sitting on your hand. |
| Balanced Forces | Pushing on a brick wall does not usually cause the brick wall to move. This does not mean your push force did not exist. There are many forces around us , but most do not cause movement. This is because the forces are balanced. |
| Balanced Forces In Tug Of War | If the forces of two people balance each other, there is no movement. The people are pushing or pulling with equal and opposite forces. Balanced forces are important. Two ends will be balanced if they pull with the same force in opposite directions. |
| Unbalanced Forces | Consider the forces acting a weight. It stays in the air because the forces acting on it are balanced. Its being pushed with the same force as gravity. To move the weight up, you use a force stronger than gravity. Making forces on the weight unbalanced. |
| Evidence Of An Unbalanced Force | There are three ways you can tell if a force is unbalanced. Forces are unbalanced if there is a change in the speed, direction or shape of an object. |
| Evidence Of An Unbalanced Force On Rope | A rope is still, so all the forces are balanced. If two people are pulling equally in opposite directions on a stationary object, then its balanced. If there's an imbalance, then the object will move. The change in motion is due to its unbalanced. |
| Evidence Of An Unbalanced Force On A Soccer Ball | If a ball is resting on the ground, then all the forces acting on it are balanced. Consider a soccer ball rolling towards the goal. If the goalkeeper kicks it away, then the ball will change direction because the goalkeeper’s kick unbalanced the forces. |
| Evidence Of An Unbalanced Force On Playdough And Change In Shape | Play dough sitting on the bench will not change unless you add a push force with your finger. Your finger unbalances the forces. The evidence for this unbalanced force is a change in shape. |
| Representing Forces | Force diagrams can be represented using an arrow. A short arrow shows a weak force, and a long arrow shows a strong force. The direction of the arrow shows the direction of the force. |
| Forces Can Be Added Together | When trying to lift a heavy object , you won't succeed because the force you exert would be too weak. But if a few of your friends helped you by adding their force, the combined forces would be stronger than the pull of the Earth. |
| Net Force | Net force is the combination of the forces on the object. If the object is lifted, the forces are unbalanced and the net force on the object is upward. |
| Calculating Net Force | If an object is stationary or moving at a constant rate in the same direction, then the net force is zero and the forces are balanced. If an object changes it speed, shape or direction, then a net unbalanced force must be acting on it |
| Calculating Net Force | Two people are pushing ,one with 200N and one with 150N if they are pushing together in the same direction to the right them its 350N to the right. If they are pushing in opposite directions it would be 50N to the direction in which the 200N is pushing |
| Contact Forces | Some forces make objects move because of a direct push or pull. It is much easier to move a pencil if you push it with your finger. Your finger must touch the pencil or be in contact before the pencil will move. This is called a contact force. |
| Non Contact Forces | Forces can cause movement without touching which are called non-contact forces. An example is the magnetism between a magnet and a metal. When a magnet is held near a metal, the paperclip is pulled towards the magnet. There is no touching, or contact. |
| How Magnets Push And Pull | Magnets are made out of an alloy. Magnets are said to have two magnetic poles –north (N) and south (S). If you hang a bar magnet from its centre by a piece of string, the north end will swing to point north. |
| Alloy | A mixture of metals. Bar magnets used in most schools are usually made of the alloy alnico, which is iron mixed with aluminium, nickel and cobalt. Strong magnets are made from metals known as ‘rare earth’ metals. They are much stronger than normal magnets |
| Attraction And Repulsion | The two unlike poles (a north and a south) attract each other. When two like poles (two north poles or two south poles) are placed together, they push each other apart. This is called repulsion. Both forces are non-contact. |
| What Causes A Magnetic Force | Iron needles can be made magnetic by having a magnet on one side of it in one direction. The magnet pulls the particles so that they line up in one way. Stroking the needle line up the particles which makes the domains point in one way making it magnetic |
| Domains | Larger sections of the magnet called domains point in the same direction in a magnetic object. When most of the domains are pointing the same way, they can pull or attract a metal. Dropping the magnet can cause the domains to become mixed up. |
| Permanent Magnets | Some magnets never lose their magnetic force. The domains are often arranged while the metal is buried under the ground. Breaking them does not change the arrangement of the domains. The two become smaller magnets with the same forces as the original |
| Magnetic Train Tracks | The forces of magnets are used in the design of magnetic train tracks. Electro magnets with like poles on the train and track make the train float. To move the driver changes the pole of the train magnet, and the track magnet pushes the train. |
| Magnetic Field | The space surrounding a magnetic material/source. In the space it pulls and pushes other magnets. The power of the force depends on how close the magnet is. The closer the magnet is the stronger the force, the further the magnet the weaker the force |
| Natural Magnetic Field Of Earth | Created by the geo dynamo. Its a big generator inside the Earth that produces its magnetic field. It acts like a shield to keep harmful particles from the sun (solar wind) from hitting the Earth's surface. The magnetic field deflects these particles away |
| Example Of Magnetism In Real Life Situations | Another Real-life example of magnetism is the separation of aluminium and magnetic metal objects. This is done by a large moving magnet that attracts the metal but not the aluminium. |
| How A Compass Works | It detects and responds to the Earth's natural magnetic fields. Such as the north pole. If the compass doesn't have any other magnets pulling on it the needle in the compass will always point north. |
| Electrostatic Forces and Charge | When two objects rub against each other a small electrical charge builds up, one object becomes positive while the other becomes negative. The two charges act like the north and south poles. Charged objects attract uncharged objects |
| Electrostatic Forces Present In Everyday Situations | Attraction of a plastic wrap after you removed the wrap. Lightning after or is striking the ground. When you rub a balloon your head and our hair sticks to the balloon. A photocopier and laser printer operation. |
| Unlike and Like Electrostatic Forces | Following the same rule as magnetism, two unlike charges will attract while two like charges will repel |
| Electrostatic Forces And Magnetic Forces | Both forces are non-contact. However electrostatic forces can act on stationary particles. In magnetic forces, the charged particles have to be already be moving once they enter the magnetic field in order to get a magnetic force. |
| Gravity | Gravity is a force that attracts objects towards the centre of the Earth. It is known as the invisible force that keeps our solar system together, without it we would be dead. |
| Gravitational Field | A Gravitational field is a force that exists in a group of mass. Everybody with matter in a universe attracts other bodies of matter toward itself with the ability of a gravitational field. |
| Mass And Weight | Mass is a measurement of how much matter an object contains. While weight is the measurement of gravitational force on an object |
| Weight Formula | The formula for calculating weight is: mg (mass times gravity). |
| Why does weight not affect the acceleration of an object during a fall? | It is because weight, mass and size does not affect Earth's gravitational pull so they fall at the same speed than all other substances; Earth pulls on something with the same amount of force |
| High Tide | When water rises to its furtherst on the shoreline. When the area in which the shore is facing the moon directly and the moons gravitational pull makes the water tide rise up. However as the earth rotates the tide goes back so high tide is about 12 hours. |
| Low Tide | Low tide is when the area in which the shore is facing away from the moon so this is when the moons gravitational pull is weakest which leads to the oceans water level to lower. Low tide is opposite to high tide. |
| Neap Tide | A neap tide is during the time after the first or third quarters of the moon when there is the least amount of difference between low and high water. |
| Spring Tide | A spring tide is after either a full moon or a new moon this is when there is the greatest difference between high and low water |
| Forces In Surfing | Surfing is a sport of force which used the force to move along the waves because of the speed and force of the strong waves. Also when paddling onto the wave you use the force to push the water behind and paddle forward. |
| Forces In Swimming | Swimming is a water sport where people use, drag, lift and buoyancy. You drag your arms in the water to push and gain force in the water to accelerate. |
| Forces In Tennis | Tennis you have to push the ball away from you and making the ball going faster to the opponent gravity is also a force because drags the ball down |
| Friction | Friction is the force that resists movement between two objects in contact. Friction generally slows down moving objects. |
| Friction In Sport Shoes | When buying sports shoes, many people look for shoes with good grip. This grip prevents the shoe from sliding when they run and helps to avoid sliding when they stop. The grip provides friction between the ground and the wearer. |
| Friction In Movement | Friction slows everything down that is moving. It acts in the opposite direction to the movement. The greater the friction, the more the movement slows down and eventually stops. |
| How Does Friction Work | Friction is when objects rub. When you walk you rely on the shoe rubbing against the ground so that you can push forward. When you stop you rely on the friction to stop your movement. With no friction your feet would slip on the ground like walking on ice |
| Evidence Of Friction | When a movement is slowed down its because of friction. Without friction a bike would keep rolling along a road without pedalling. A pen/pencil would slide over a page with no mark. Friction is very useful, but also creates issues so we try to reduce it. |
| How To Decrease Friction With Rollers | Rollers or balls are one way to reduce friction. Because the balls roll across the ground, it is much easier than being dragged along. Tiny balls are often used as bearings to allow two surfaces to slide over one another easily. |
| How To Decrease Friction With No-Contact | Hovercrafts and air pucks have low friction because they use a layer of air to glide. There is no contact and so almost no friction. The same with magnetic levitation trains, where the train carriages are held above the tracks by strong magnetic forces |
| Lubricates And Lubrication | Lubricants work by coating the surface with an oily/greasy substance, which makes it slippery. Examples could be candle wax or soap on bicycle chains on the wheel axles makes the wheels spin more easily, with less friction. |
| Air Resistance/Drag | Air resistance/drag, is the friction between a moving object and the air it is moving through. When the object moves it needs to push the air particles limiting the speed of the object. Parachutes use air resistance to slow the movement of the falling. |
| Streamlining | While this is an advantage it you are sky diving, it can be a problem for cars and trucks. The greater the air resistance, the more fuel the car will use. Streamlining (making the surface smooth and rounded) helps to overcome air resistance. |
| Streamlining In Sharks | Fish and sharks have streamlined bodies. This allows them to move through the water with the least amount of friction. |
| Simple Machines | Ancient Egyptians, Romans and Greeks understood forces well. They made simple machines that helped them to build the pyramids, fight wars and build cities. A simple machine is used to decrease the amount of effort to do the work |
| Levers | A simple machine such as scissors, pliers, brooms, shovels, wheelbarrows and can openers. A lever is a solid rod or bar that is supported at a turning point called a fulcrum. The force used is called the effort, and the resisting force is called the load |
| Levers In A See-Saw | When a person on a see-saw is goes down the other is goes up. The weight doesn't need to be equal to work. A person can lift a heavier weight by moving away from the fulcrum. A person 2m away from the fulcrum can lift two people who are 1m away. |
| Mechanical Advantage | The lever gives you a mechanical advantage. The size of the advantage can be calculated by dividing the size of the load by the size of the effort: |
| Magnification Of The Force | Magnifies the force. When the small force is magnified into a bigger force so a bigger load can be lifted with little effort however the effort section of the lever must have a greater distance to move the load a shorter distance; scissors, end of hammer |
| Distance Magnifiers | Opposite of force magnifiers. Magnifies the distance instead force. So a little distance on the effort can move the load a long distance. However the effort section must have a greater force to the load a greater distance. Also known as speed multipliers |
| Types Of Levers | There are three types of levers, and they are classified according to the position of the fulcrum (turning point). First, second and third class levers |
| First class levers | A type of lever in which the fulcrum is between the effort and the load. Example could be a see-saw or scissors. Good for lifting large loads with little effort since first class levers are also force magnifiers |
| Second Class Levers | A type of lever in which the load is between the effort and the fulcrum. Example could be a wheelbarrow when you lift by holding the handle (effort) to carry the barrow (load) and the turning point is at the wheel (fulcrum). They are also force magnifiers |
| Third Class Levers | A type of lever in which the effort is between the load the fulcrum. Example could be a tennis racket because you are swinging your wrist (fulcrum), the handle (effort) and the racket is hitting (load). They are also also distance magnifiers |
| Aboriginal And Torres Strait Islander Levers | Many Aboriginal and Torres Strait Islander Peoples understand the advantage of levers in hunting. |
| Woomera | The word comes from the Dharag language and refers to a spear thrower that can launch a spear further and with more force and with more acceleration. |
| Aboriginal And Torres Strait Islander Spears | A spear is fitted into 50-100 cm long lever and held in place with a peg. The person throwing the spear holds the woomera and swings it over their head. This makes the lever arm longer, moving the spear faster, increasing the speed and accuracy |
| Type Of Levers In Aboriginal And Torres Strait Islander Levers | Depend on the position of the fulcrum. If the wrist is used to flick the spear, then this becomes the fulcrum. If the arm and wrist remain straight, and the motion is like a bowler (in cricket), the fulcrum is located between the thrower’s shoulder blades |
| Forces Acting On The Aboriginal And Torres Strait Spears | Once the spear has left the spear thrower, the unbalanced forces of air resistance cause the spear to slow down and the force from the Earth’s gravity causes the spear to fall. |
| Different Styles And Shapes Of Spears In Aboriginal And Torres Strait Islander Levers | Longer spear throwers can increase the speed more than shorter spear throwers. This increase in speed means that the spears used need to be lighter. |
| Force Multipliers | For these levers the effort arm is longer than the resistance arm |
| Speed Multipliers | For these levers the resistance arm is longer than the effort arm |
| One Pulley System | The system changes the direction of the force not the size. As a person pulls down on the rope, the weight on the other end moves up. This does not change the amount of effort needed, but it makes lifting easier as the person can use their weight. |
| Mechanical Advantage Of A Pulley | The mechanical advantage is calculated by the number of ropes between the upper and lower pulleys. However when calculating the effort or load the formula is still Load/Effort |
| Examples Of One Pulley | You have probably used this type of pulley when you pull the cord to open a window blind at home |
| Two pulley system | The more pulleys that are used, the easier it is to lift a load because its mechanical advantage is increased. If two pulleys are used, the system can lift twice the load of a single-pulley system. The mechanical advantage of this system is 2. |
| Four Pulley System | It can magnify the effect of the effort four times. For example, a 25 kg effort can lift a 100 kg load in a frictionless pulley system. This system has a mechanical advantage of 4. |
| Block and Tackle | Groups of pulleys are often mounted together in a frame or ‘block’. This device is called a block and tackle. A small effort pulling through a long distance lifts a large load through a much smaller distance (force magnifier) |
| Examples Of Pulleys | Garage door, blinds, wells, curtains, crane |
| Force Required In A Pulley | Mass/Mechanical Advantage |
| How Far The Mass Would Be Raised In A Pulley | Length of rope/Mechanical Advantage |
| Length Of The Rope In A Pulley | How Far The Mass Would Be Raised X Mechanical Advantage |
| Ramps | Ramps are the simplest types of inclined planes. A ramp is used to lift heavy objects (the load) up to a higher level or to bridge gaps between uneven surfaces. Going up a ramp will take longer than a step up but requires less force from your legs |
| Examples Of Ramps | A piano mover might use a ramp to get a piano from the ground onto a truck. Escalators are moving ramps with steps. |
| Wedges | An inclined plane that moves through another object and changes the direction of a downward force to a sideways force. |
| Examples Of Wedges | An axe when it hits a log, the downward force is changed to a sideways force, which splits the log. Humans discovered the benefits of wedges when they used the jagged edges of rocks to cut animal flesh and skin. Other examples are a knife or teeth |
| Screws | An inclined plane. Screws penetrate materials such as wood or cork by using the turning effect of a force. The effort needed to turn a screw into an object is much less than that required to hammer the screw into the same object. |
| Thread | The indent that spirals around a screw, called the thread, looks almost like a road (a ramp) spiralling up the side of a mountain. |
| Wheels And Axles | A wheel is a type of lever that turns in circles about its centre –the fulcrum or pivot point. An axle usually links the lever and the wheel. |
| Examples Of Wheels And Axles | Circular door handle. For example, when you turn the doorknob, you apply an effort force to the door handle and the axle exerts a force on the load (the latch), which opens the door. Another example could be a ferris wheel |
| Wheels And Axles As A Force Magnifier | You apply a small effort to a doorknob to move a larger load, the latch. This is because the outside edge of the wheel, or doorknob, moves a larger distance than the axle, or latch. |
| Wheels And Axles As A Force Magnifier | When you pedal a bike, you apply a force to the pedals. This force causes the larger wheels to turn. The distance the wheel travels is much further than the distance the pedal travels. The distance has been magnified. |
| Describe what happens to the magnetic properties of a magnet when it is broken into two? | The magnetic properties stay the same as the domains do not change arrangement giving the magnet its usual magnetism |
| Identify the class of lever that is formed by the upper torso. | First Class lever |
| Tension | The state of being stretched tight. Also the force that stops the rope/string from pulling apart |
| A skydiver jumps from an aeroplane and falls downward because of the Earth's gravitational pull. Identify what happens to the Earth in response to the skydiver. | It moves up, but only an extremely small distance because of its much larger mass. All masses have a gravitational pull. Its because the earths gravitational pull is so much stronger so you can't notice the skydivers gravitational pull on the earth. |
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