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the distance- time graph will become steeper. Motion (movement) at a constant speed is Distance-time graphs- speed: Aan object's speed is shown by the gradient (slope) of the distance - time graph The slope (gradient) of the distance- time graph will become less steep... Distance on the y-axis If an abject's speed increases, the object will Increasing speed travel a longer distance in the same amount of time. If an object's speed decreases, then the Decreasing speed object will travel a shorter distance in the same amount of time. On a distance - time graph, if the object becomes stationary, the line becomes horizontal The Speed-time Cor time) velocity gradient is acceleration Time on the x-axis graphs Speed on the y-axis. Speed-time graphs A horizontal line above Velocity time graphs Time on the x-axis. If an object's speed is constant, then the speed-time graph will be horizontal. If the object is not moving (is at rest), the graph will run along the x-axis because that is where y=0. under Area how a Velocity -time Graph Object is moving at a constant speed. 7 Velocity on the y-axis. Acceleration determines. the change in speed. If the speed of an object increases with time, its graph will have a positive gradient.. If an object slows down, its graph will have a negative. constant constant An objects acceleration describes its in If change speed. the speed of an object increases with time, its graph will have a positive gradient. If an object slows down, its Area of a rectangle. The area of a rectangle = base X1 x height speed M Constans graph base Base will the x-axis means the The area under a velocity- time graph is equal to the distance travelled by an object. To find the area under the graph, break it down into small shapes and add the areas of the shapes. Area of a triangle The area of a triangle = 0.5 x base x height height have height deceleration time (s) a negative gradient. The total area under a speed-time graph is the distance that the object. has travelled. Speed + acceleration. Average speed The average speed is the total distance travelled divided by the total time taken. We can measure speed using light gates. It is usually measured in mls The trolley is rolled down a ramp so that the card passes through the light gate. Equation Average Speed The length of a peice of card is measured Experiment - light gates with a ruter, and attached to a trolley I is the length of the card and t is the amount of time it takes to pass through the gate. Light gates record how long it takes for an object to pass through them.. So can be used to calculate the speed: Equation for Average Speed: Average a = Speed Equation for Acceleration Usain Bolt brake a world record when he ran 100m in 9.58 seconds. What was his average. speed? 100 9.58:10.4m/s Average speed = total distance = total time Experiment - light gates gate is calculated using v=x = t +v== time taken The speed of the trolley when it passes the time taken Uniforn Acceleration v²²:20s final velocity squared minus inith verby squared is equal to 2 times the distance times the acceleration • Velocity, distance and acceleration v². 2 = 20s minus The final velocity ant 2 times the acceleration times by the distance. the The final velocity is equal to the inital velocity plus the acceleration times by time. equals A ball rolling down a hill accelerates uniformly from rest to a velocity of 5mils in 10 seconds. What is the acceleration of the ball? 5÷10:0.5m/s² •Useful equations 2 very useful equations which can be used to solve problems involving constant acceleration... Final speed: inital speed + (acceleration & time) →v=utaxt or v=ut at (Final speed)² - (inital speed)² = 2 x acceleration x distance. √²-₁² = 2 xaxs or v²-u²2x03 Decele. Deceleration is negative acceleration. Average speed = total distance = tubal time. Acceleration Newton's Laws Force and Acceleration A force may cause a mass to accelerate. This acceleration can be a change in speed, a Change in direction or a change in both speed and direction. The change in an object's motion is caused by the resultant force Resultant force Forces acting on an object are unbalanced (not equal Resultant force (F): mass (m) x acceleration (a) Acceleration is measured in metres per second squared speed Acceleration is equal to change in velocity divided by time taken. This is Newton's 2nd Law. 7 is the sum of all of the forces ucting on an object. The resultant force acts on the object. Resultant force equation F=ma ✓ resultant force causes an acceleration. Acceleration can be calculated with this equation resultant force = moss & acceleration Newton's 1st Law 12 States: The velocity of an object will only change if a resultant force is acting on the object. This applies to a stationary (still) or moving object. Stationary (still) If an object is stationary (not moving / still) and there is no resultant force acting on it, it will stay stationary. Moving If an object is moving and there is no resultant force acting on it, the object will continue moving in the same direction at the same speed. This means that the object will continue moving at the same velocity. → This also means that the velocity of an object will only change if a resultant farce is acting an the abject.. Newton's 3rd law. Example: Force of table of arrow Force of arrow on table States: Whenever 2 objects interact, the forces that they evert on (opply to each other are equal and opposite. If one object exert (applies) a force on another object, then the other object must be exerting (applying) a force back. → If a hand pushes on a table, the table will push back on the hand with an equal force, but in the opposite direction. Newton's 2nd Law Defined by the equation: Resultant force (f) = mass (m) X acceleration (a) Newton's hand Taw Peartes Newton's 1st Law. Where there are balanced forces, there is no resultant force Contact + Non- contact forces. A force is a push or pull that acts on an object when it interacts with another Object. All forces objects are either: Contact forces Happen when two objects are physically touching → push friction, wir resistance, tension and normal contact force are all examples of contact forces F Non-contact forces Happen when objects are seperated (not touching) → pull Gravitational force, electrostatic force and magnetic force are all example of non-contact forces... An interaction pair is a set of 2 forces that are equal and opposite, acting on 2 interacting. objects. Contact forces Two objects are physically touching Examples: Tension The pulling force that a string or cable exerts (creates) when something or someone pulls on it. Air resistance Comes about when. This create Normal contact force When you push on a table, your hand doesn't move through it. This is because the normal contact force from the table pushes equally on your hand. Friction an object moves through air and collides with (nits) air molecules. a force that slows the object down.. Comes about whenever two surfaces are touching and trying to move against each other. Tiny bumps in the surface interlock loverlap or fit together). This creates a frictional force that opposes their motion. Friction acts in a direction apposite to an object's direction of motion (travel) Friction and Air resistance: fidget spinners reduce friction to the lowest level possible to let them spin for as long as possible. Allow them to move move freely. across each other Opposes an object's motion. Friction finns Air resistance opposes motion and often causes heating. force created by two surfaces rubbing against each other... seperates two surfaces with a thin layer of oil can reduce friction A frictional force Examples: Electrostatic force Gravitational force Magnetic force Mass + Weight The mass of an object is a measure of the amount of matter it contains. The mass of an object M is constant. It is the same on Earth, on the moon and in space. Mass Amount of matter An object's mass is a measures of the amount of time it contains. It is the same wherever you go. It is a measure of the amount of matter in an object. Equation for Weight weight = mass & gravitational field sirength Weight weight is measured in newtons An object's weight is different on different planets = mass & gravitational field strength weight= me -Free fall then the object's If an object in free fall, will accelerate Equation for mass weight gravitational field strength facts : muss Definition of weight. The force acting downwards in an object due to gravity. weight is the only force acting on it. The weight of an object is the force that acts downwards on an object due to gravity. Acceleration due to gravity Am object in free fall will accelerate at a constant rate. This constant rate is called the accele- ration due to gravity (g) The average value for acceleration on Earth due to gravity is 9.81m/s², but we round up to 10 m/s² in most calculations. Falling with Air Resistance * Objects falling through the Earth's atmosphere do not continue to accelerate inde- finitely because air resistance slows them down. Frictional Force Air resistance is a frictional force that opposes the motion of objects moving quickly thro- ugh air. -Slows a falling object. Slows a falling object. Force due to air resistance increases us the speed of a falling object increases. Opposes all motion through air Slows a moving object Air resistance Examples Base jumping: the weight of this bose jumper is the only force acting downwards. Air resistance Slows u falling down object free fall If un object is in free fall, then the object's weight is the only downward force acting on it. Car off cliff: only force on this car, for the time is in free fall, is its own weight. To say an object weighs 67kg. is to describe its mass. Weight and Mass Weight changes on the moon us on Earth is proportional to the speed of the falling object. Air resistance Stages describing how air exerts a resistance force on a moving object: 1. As an object moves through air, it must push the air aside to move. 2. This force needs, and so the object exerts a force on the air. 3. Every force and opposite reaction, so the object is slowed Weight is measured in Newton's Mass is constant on different planets. Mass is different to weight. Stopping Distance Stopping distance is the distance it takes a car to stop in an emergency (ie. when the car is braking suddenly). Stopping distance: thinking distance + braking distance < 2 elements to the overall stopping distance. During The time this reaction time, the carries on moving picar The time it takes for a driver to react to a The thinking distance is the distance Thinking distance situation is their reaction time. travelled between when the driver realises they need to brake and when they apply the brakes. Wesend Distractions Cause a driver to react more. in an emergency → phones. slowly For a car travelling at 50mph, a typical Stopping distance is 5.3m For a car travelling at 70mph, a typical stopping distance is 96m. factors affecting thinking distance The 3 factors. Distractions Braking distance Tiredness Inital car speed →→→ the faster a car is travelling, car on the motorway: 31m/s Wind: 6m/s Condition of car → If a car's brakes or tyres are in a poor condition, then the braking distance will increase. the further it will bravel before it comes to a sep Factors high Rood conditions → Wet or icy conditions will increase The mass of the vehicle, larger the stopping distance will be. the braking distance. More friction there is between the tyre and the road the shorter the stopping distance will be. 50 km/h = 13.9 m/s. The distance the car travels between the driver applying the brakes and the car stopping Typical stopping distances distance is 12m Factors Drugs or Alcohol → under the influence of drugs. more slowly- in an emergency. Reaction Times Sound: 330m/s Air: 340m/s Typical Speeds For a car travelling at 20mph, a typical stopping Tiredness Tired drivers will react more slowly in an emergancy. factors affecting braking distance. 50 km/h: (50x1000) 3600 ml seconds. Increase reaction times. Conversion of units Alcohol or alconal will reace. walking :1.4m/s running: 3.3mls bus in town: 10m/s. 50 km/h: 50 x 1000 metres/hour Valid units for speed: kmls km/h m/s We can measure human reaction times using the ruler drop test. Dangers of Large Decelerations The greater the braking force, the greater the deceleration of the vehicle. Large decelerations can cause brakes to overheat and/or the car to said. A larger deceleration will transfer more stopping force to passengers. This harms passengers. Traffic lights When a typical family cars decelerates at a set of traffic lights, only a small force is exerted on (applied to) the passengers.. This is because the deceleration happens over a The force does harm the passengers. · Emergency stop When a typical family car suddenly stops in the road to avoid a collision, a greater force is exterted on (applied to the passengers. This is because the decelerations happens over The force Should not be enough to harm the passengers.. Long period of time. Crash crash, When a typical family car suddenly is stopped by a foor Force C Shorter period of time.. passengers than the emergency stop This is because the deceleration happens in even less time. This could harm passengers. X What is the braking force required to stop a car of mass 500kg from an inital speed of m/s in a time of 4s? 500 × 2 4÷4:250 N time an even greader force is applied to the Equation for calculating the change in momentum Elastic + Inclassic An elastically deformed an object will return to its original shape when the force stops. An inelastically deformed object will not return to its original shape when the force stops.