# Force, Motion and Energy

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• Forces, Motion and Energy
• Resultant Forces- "overall force"
• E.g Car engine moving car left. Air resistance moving right. The difference = resultant force
• Resultant force not 0= accelerating or decelerating
• Resultant force 0 = stationary or steady speed
• Distance Time Graphs
• Flat line (no gradient) = stationary
• Calculating speed from distance time graph (2 methods)
• Speed= distance / time
• eg 10m in 20 secs. Speed = 10/20. Speed = 0.5 m/s
• Units of speed = m/s
• Gradient method. Difference in y / difference in x
• Velocity Time Graphs
• Acceleration = (final velocity - initial velocity)/time
• acceleration = m/s^(2)
• eg A car goes from rest to 30m/s in 5 seconds
• (30-0)/5 = 6m/s^(2)
• Analyzing graph
• Steeper gradient = greater acceleration
• Calculating acceleration from velocity time graphs;
• Difference in y/ difference in x
• Calculating distance travelled
• Area bellow the graph. Units in m
• Calculating Acceleration: (2 formulas- pick most suitable)
• Acceleration= (final velocity-initial velocity)/time
• Acceleration= Force (resultant force)/mass
• Terminal Velocity
• When speed increases, air resistance increases.
• 1) Person falls out of plane. The force of weight (mass x gravity) is greater than the force of air resistance. = acceleration towards earth
• 2) As speed increases, air resistance increases. till forces are balanced= steady speed= TERMINAL VELOCITY
• 3) Parachute opens. Person slows down (decelerates) because air resistance increases
• 4) Forces Balance eventually= TERMINAL VELOCITY
• Forces on Elastic Objects
• Work done= Energy Transferred
• Hookes Law simplified "The more force applied, the more and elastic object will stretch provided you do  not pass the limit of proportionality"
• Force= Spring constant x extension
• Force=( N). Spring constant =(N/m). Extension= (m)