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Forces and Acceleration

Learn about the relationship between force and acceleration, and understand how the size of a force affects acceleration. Explore the concept of resultant force and how it impacts the rate of falling objects.

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Forces and Acceleration

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  1. 04 January 2020 Today’s Title: CW: Forces and acceleration Learning Question: How is acceleration related to the size of a force? Who will drop to the ground faster, and why? http://www.bbc.co.uk/learningzone/clips/acceleration-and-force/25.html

  2. Aims • Able to give the correct units for force, mass and acceleration • Able to state newton's second law. • Able to use newton's second law.

  3. Key words… • Speed • Velocity • Displacement • Vector • Magnitude • Direction • Acceleration • Gradient

  4. Resultant force • The single force that has the same effect on the object as all the individual forces acting together.

  5. Size of the force • An object will accelerate in the direction of the resultant force. • The bigger the force, the greater the acceleration. • Doubling the size of the (resultant) force doubles the acceleration.

  6. The mass • An object will accelerate in the direction of the resultant force. • A force on a large mass will accelerate it less than the same force on a smaller mass. • Doubling the mass halves the acceleration.

  7. Draw an arrow to show the direction of the resultant force. How will drop to the ground slower? Explain why you have made your choice.

  8. Force = Mass X Acceleration F m x a

  9. Forces and acceleration calculations • You should know the equation that shows the relationship between resultant force, mass and acceleration, and be able to use it. The equation Resultant force (newton, N) = mass (kg) × acceleration (m/s2). • You can see from this equation that 1 N is the force needed to give 1 kg an acceleration of 1 m/s2. • For example, the force needed to accelerate a 10 kg mass by 5 m/s2 is: • 10 x 5 = 50 N • The same force could accelerate a 1 kg mass by 50 m/s2 or a 100 kg mass by 0.5 m/s2. • Putting it simply, we can say that it takes more force to accelerate a larger mass.

  10. Your task • Complete questions 1 – 5 from pages 234 – 235 from the textbook. • You have 10 minutes to answer these questions

  11. 04 January 2020 Today’s Title: CW: Terminal velocity Learning Question: What is terminal velocity? http://www.bbc.co.uk/learningzone/clips/why-does-a-human-have-a-different-terminal-velocity-to-a-mouse/8751.html

  12. Lesson objectives Know: what ‘terminal velocity’ means Understand: why falling things reach a terminal velocity Be able to: describe and explain the stages in a parachute jump (including the forces involved and whether or not acceleration is happening at each stage)

  13. Terminal velocity extra questions • Explain why a falling human reaches a higher terminal velocity than a falling cat. • Explain why a falling human without a parachute reaches a higher terminal velocity than a falling human with one. • Parachutes on the moon? – Comment on their usefulness. • Film of parachute jumpers often makes it look as though they shoot upwards when their parachute opens. They don’t – so why does it look that way? • Sketch a graph showing the speed of a skydiver from the moment she jumps to the moment she lands. • What possible reasons can you think of for why the exam board decided terminal velocity was important enough to be part of the Physics 2 module?

  14. Terminal velocity extra questions – outline answers • The object accelerates until the air resistance matches the weight. A human has a bigger weight, so has to reach a higher speed before the air resistance matches it. • A falling human with a parachute has a greater air resistance at a given speed, so does not have to reach as high a speed for air resistance to match weight. • Parachutes are useless on the moon, as there is no air, so no air resistance. Everything keeps on accelerating to the end of its fall. • The camera operator remains in free fall while he films the parachutist opening his parachute. At this point, the parachutist suddenly slows down relative to the camera operator, who shoots past him. This makes the parachutist appear to move upwards.

  15. Velocity-time graph for parachutist… Parachute opens – diver slows down Speed increases… Terminal velocity reached… On the Moon New, lower terminal velocity reached Diver hits the ground Velocity Time

  16. Your task • Complete questions 1 – 7 from pages 236 – 237 from the textbook. • You will be given a teston the motion and forces topic tomorrow! • Study support is TONIGHT! No excuses!

  17. Q1. What does displacement mean? • the speed of something • The speed and size of something • The total path travelled • The distance between the start and finish

  18. D

  19. Q2. What is the equation to work out speed? • Speed (m/s) = distance ÷ time • Speed (m/s) = time – distance • Speed (m/s) = distance x time • Speed (m/s) = distance + time

  20. A

  21. Q3. What information does velocity give you? • How fast something is going • The magnitude of something • The speed and direction • The path of something

  22. C

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