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Forces N Bronks

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**Distance, Speed and Time**

Speed = distance (in metres) time (in seconds) Dave walks 200 metres in 40 seconds. What is his speed? Laura covers 2km in 1,000 seconds. What is her speed? How long would it take to run 100 metres if you run at 10m/s? Steve travels at 50m/s for 20s. How far does he go? Susan drives her car at about 40m/s (136km/hr or 85mph). How long does it take her to drive 20km?

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**3/.Faster Constant Speed**

Distance-Time Graphs D t D t 1/.Constant Speed 2/.Stopped D t 3/.Faster Constant Speed

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**Distance-time graphs 40 30 20 10 2) Horizontal line = Stops**

2) Horizontal line = Stops 4) Diagonal line downwards = Back to Start Distance (metres) 3) Steeper diagonal line = Faster Speed Diagonal line = Constant Speed Time/s

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**40 30 20 10 20 40 60 80 100 Distance (metres) Time/s**

Distance (metres) Time/s What is the speed during the first 20 seconds? How far is the object from the start after 60 seconds? What is the speed during the last 40 seconds? When was the object travelling the fastest?

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**Speed vs. Velocity Speed is simply how fast you are travelling…**

This car is travelling at a speed of 20m/s Velocity is “speed in a given direction”… This car is travelling at a velocity of 20m/s east

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Distance-Time Graphs D t acceleration

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**Acceleration V-U T A Acceleration = change in velocity (in m/s)**

(in m/s2) time taken (in s) A cyclist accelerates from 0 to 10m/s in 5 seconds. What is her acceleration? A ball is dropped and accelerates downwards at a rate of 10m/s2 for 12 seconds. How much will the ball’s velocity increase by? A car accelerates from 10 to 20m/s with an acceleration of 2m/s2. How long did this take? A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration?

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**1/.Constant Acceleration**

Velocity-Time Graphs V V t t 1/.Constant Acceleration 2/.Constant Velocity V t 3/.Deceleration

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**Constant Acceleration**

Velocity-time graphs Upwards line = Constant Acceleration 80 60 40 20 4) Downward line = Deceleration Velocity m/s 3) Shallow line = Less Acceleration 2) Horizontal line = Constant Velocity T/s

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80 60 40 20 Velocity m/s T/s How fast was the object going after 10 seconds? What is the acceleration from 20 to 30 seconds? What was the deceleration from 30 to 50s? How far did the object travel altogether?

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v/m/s 2 4 6 8 t/s 1 3

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**Force causes a body to change velocity**

The unit is called the Newton (N) A few types of Forces Magnetic Force Tensile Forces Friction happens when 2 bodies are in contact.

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Friction Friction is the force that opposes motion of a body when it is in contact with another. Friction happens when 2 bodies are in contact. Lubrication reduces friction

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**Friction What is friction? Give 3 examples where it is annoying:**

Give 3 examples where it is useful: What effect does friction have on the surfaces?

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**Force and acceleration**

If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers: Force (in N) = Mass (in kg) x Acceleration (in m/s2) F A M

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