GCSE Science Velocity and Distance-Time Graphs

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Velocity and Distance-Time Graphs

• velocity has speed and direction
• speed and velocity are measured in m/s, km/h or mph
• speed is how fast you are going without direction
• velocity has the direction also
• distance-time graphs
• speed = distance/time
• the gradient tells how fast object is going
• Flat is when its stationary
• Straight uphill or downhill means its at a steady speed
• The steeper the graph, the faster it is going
• Downhill represents going back
• Curves mean acceleration and deceleration
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Acceleration and Velocity-Time Graphs

• acceleration is how quickly the velocity is changing
• change in velocity can be change in speed or change in direction or both
• acceleration = change in velocity/time taken
• Steeper the graph the greater the acceleration and deceleration
• Atrea under any section of graph is equal to the distance travelled in that time
• Curve means changing acceleration
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Resultant Forces

• resultant force is the overall force on a point or object
• there are at least two forces acting upon an object
• to work out the resultant force, you add or subtract the forces
• if there is a resultant force then the object will change velocity, change its position
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Forces and Acceleration

• if the resultant force on an object is zero, the object will remain stationary
• if there is no resultant force on a moving object, it will remain at the same velocity
• a resultant force means acceleration
• if there is a non-zero resultant force, then the object will accelerate in the direction of the force
• any resultant force will produce acceleration, the formula is F=ma or a =F/m
• m: mass in kilograms (kg)
• a: acceleration in metres per second squared
• F: is the resultant force in Newtons (N)
• reaction forces are equal and opposite ( two forces are acting on different objects)
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Frictional Force and Terminal Velocity

• friction slows things down
• if an object has no force it will slow down and stop because of friction
• friction acts in the oppoiste dtrection to movement
• to travel at steady speed, driving force needs to balance frictional forces
• you get friction between two surfaces in contact, or when an object passes through fluid (drag)
• most resistive forces are caused by air resitance or drag
• most important factor to reduce drag in fluids is keeping object streamlined
• drag increases as speed increases
• objects falling through liquids reach a terminal velocity
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Frictional Force and Terminal Velocity II

• when falling objects set off, gravity much more than frictional force slowing down, so accelerate
• as speed increases the friction builds up
• this reduces the acceleration until frictional force is equal to the acceleration force, then it wont accelerate anymore
• it will have reached its terminal velocity and will fall at a steady speed
• if there was no air resistance, all objects would fall at the same speed as gravity acts upon all objects
• on earth, air resistance causes things to fall at different speeds and terminal velocity is determined by drag in comparison to weight
• frictional force depends on shape and area
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Work and Potential Energy

• when force moves object through a distance energy is transferred
• Work done = Force * Distance
• gravitational potential energy is due to height
• Gravitational Potential Energy = mass * g * height
• this is measured in joules
• this is the energy that an object has by virtue of vertical position and gravitational field, when an object is raised vertically, work is down against the force of gravity and object gains gravitational potential energy.
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Kinetic Energy

• kinetic energy is of movement
• anything that is moving has kinetic energy
• Kinetic Energy = 1/2 * mass * speed squared
• kinetic energy depends on mass and speed
• the more it weighs and the faster its going, the bigger the kinetic energy will be
• to slow something down, the kinetic energy needs to be converted into other types of energy
• conservation of energy states that energy can never be destroyed or created only converted into different forms
• 1/2mv(squared) = F * d
• m: mass of car
• v: speed
• F: maximum force
• d: breaking distance
• when something falls its potential energy is converted into kinetic energy
• so the further it falls, the faster it goes
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