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PHYSICS UNIT 4 - FORCES & MOTION (Distance-Time Graphs (Curves…
PHYSICS UNIT 4 - FORCES & MOTION 
Newton's Laws of Motion
Newton's Second Law
The larger the resultant force on a object the more the object accelerates - force & acceleration are directly proportional
Acceleration is inversely proportional to the mass of an object - so object with larger mass will accelerate less than one with smaller mass.
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Newton's Third law
= Force always in pairs, equal in size, opposite in direction
If you push a shopping trolley, the trolley will push back against you, just as hard.
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Eg. skater A pushes skater B & feels an equal & opposite force from skater B's hand (normal contact force). Accelerate away from each other but skater A will accelerate more because has smaller mass.
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Newton's First Law
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If resultant force (several different forces all at once) on a stationary object is zero the object will remain stationary (balanced force). If resultant force on moving object is zero it will carry on moving at same velocity (same speed & direction)
A non-zero resultant force will always produce acceleration (or deceleration) in direction of the force.
Acceleration can take 5 different forms: starting, stopping, speeding, slowing down & changing direction.
Safety in public transport
Human reaction times - measure with ruler drop test
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Important Word meanings
Random errors - variations that are expected and anticipated in certain processes. They're often associated with measurements and transfers.
Systematic errors - bias or special cause errors. These types of errors are always in one direction. Eg. a machine dispensing a liquid may always dispense a volume that's below the desired amount due to a problem of some sort. Problems range from faulty equipment to a poorly trained employee.
Reproducible - A measurement is reproducible if the investigation is repeated by another person, or by using different equipment or techniques, and the same results are obtained.
Directly Proportional - Directly proportional means that the rate of increase in one variable is the same as the rate of increase in the other variable. If you double one thing, the other thing doubles.
Vector-Scalar Distinction
Vector
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Eg. If walk 5m north, then 5m south, displacement is 0m but distance travelled is 10m
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Everyday Speeds
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Acceleration
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Deceleration is negative acceleration, change in velocity is negative
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Estimate Accelerations (or Decelerations)
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Distance-Time Graphs
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If object changing speed (accelerating) you can find its speed at a point by finding gradient of the tangent to the curve at that point.
Gradient = speed (the steeper the graph, the faster the object is going) Speed = distance ÷ time
If object moves in straight line, its distance travelled can be plotted on distance-time graph.
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