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FORCES. FORCE: The cause of motion The cause is either a –Push or a –Pull.

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Presentation on theme: "FORCES. FORCE: The cause of motion The cause is either a –Push or a –Pull."— Presentation transcript:

1 FORCES

2 FORCE: The cause of motion The cause is either a –Push or a –Pull

3 FORCES ALWAYS COME In pairs

4 Big Science Idea Forces can affect motion in several ways: → They can make objects start moving → They can make objects move faster → They can make objects move slower → They can make objects stop moving → They can make objects change direction → They can make objects change shape

5 Forces are measured in Newtons SI unit of force Symbol: N Measured by using a spring scale

6 FORCE FACTS: → Forces are measured in Newtons (N) → Forces usually act in pairs → Forces act in a particular direction → Forces usually cannot be seen, but their effects can

7 Kinds of Forces Gravity force that pulls down toward earth (or another large object) Weight force an object has due to gravity

8 Kinds of Forces Applied Force force of one object pushing on another object Normal Force force of an object pushing back

9 Kinds of Forces Buoyant Force – force of a fluid that holds an object up (works against gravity) Tension – force pulling in two directions

10 Kinds of Forces Friction force that slows down moving objects Air Resistance force that slows down moving objects

11 Magnetism Electricity

12 Newton’s Laws First Law – Inertia Second Law – Acceleration, Force & Mass Third Law – Action-Reaction

13 First Law Inertia –An object at rest [not moving] remains at rest unless acted on by a force [push or pull] –An object in motion remains in motion unless acted on by a force [push or pull]

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15 First Law Inertia & Mass –Mass is the amount of matter in an object –The more MASS an object has, the more INERTIA the object has. –Bigger objects are harder to start & stop little inertia BIG INERTIA

16 Play video segment Newton’s Law Video segment 1 Write down examples of 1 st law in motion. After clip, share examples.

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18 1 st law of motion Purpose: to find out if mass (g) affects an object’s inertia Hypothesis: If an object has ________ mass, then it will have _______ inertia. The reason is _____________________. Procedure: Do each activity 5 times

19 Wacky Washer Stack 4 washers one on top of the other Aim one washer at the bottom of the stack Push the washer toward the stack Aim 2 washers at the stack Push the washers toward the stack Repeat with 3 washers Explain how the observations relate to the 1 st Law of Motion

20 Data Table – Wacky Washers Whathappensto thestack ofwashers Number of washers pushed into the stack Trial 1Trial 2Trial 3Trial 4Trail 5 1 washer Example: Bottom washer came out of stack and slid ____ cm. Diagram. 2 washers 3 washers

21 Wacky Washer Analysis Explain why it is possible to knock out the bottom washer only in the stack in terms of Newton’s 1st Law (If you didn’t get these results think about what went wrong). Is it easier or harder to do the trick with a larger stack of washers? Why is this so?

22 Balancing Act Balance the penny on a paper circle on the tip of your finger Remove the paper without moving the penny

23 Balancing Act Analysis Would the trick be easier or harder if instead of the penny you used a a) dime b) quarter

24 Card Trick Place card on top of cup. Place washer on top of cup. Quickly slid card out and washer should land in cup.

25 Stop! Lesson Ends Here If time allows, students can read Textbook M pages Complete Math Focus Classwork only Return textbooks

26 2 nd law of motion F=ma Force= mass x acceleration

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28 more mass=more force F= ma F= 2 kg times 2 m/s 2 = 4 N F= 5 kg times 2 m/s 2 = 10 N

29 10 N 20 N 5 kg 5 kg

30 more acceleration = more force 2 1 kg X 10 m/s kg X 100 m/s 2

31 Title: Newton’s 2 nd Law of Motion Purpose: How does mass affect force? Hypothesis:

32 Equipment: 1 toy car6 washers balance 20 cm masking tape meterstickwooden ramp Procedure: 1. Set up a ramp using the wooden ramp. Place one end of the ramp on some books or against the wall. Tape the end of the ramp on the floor. 2. Measure the mass of the toy car.

33 3. Place the toy car at the top of the ramp. Let the car roll down the ramp. Do NOT add any additional force. Use a meter stick to measure how far the car rolled. Repeat this step for trials 2-5. DO NOT PUSH THE CAR ! 4. Tape to washers to the toy car. Mass it. Repeat steps 2 and 3.

34 5. Tape 4 washers to the toy car and repeat. 6. Tape 6 washers to the toy car and repeat. Dependent variable: Independent variable: Constant variables:

35 Quantitative Data Title: The Impact of Mass on Force Mass of car (g)Force of Car (measured by how far car travels in meters) Trial 1Trial 2Trial 3Trial 4Trial 5Average 0 washers Mass = ______ 2 washers Mass = ______ 4 washers Mass = ______ 6 washers Mass = ______

36 Qualitative Data

37 Graph

38 Graph Analysis

39 Conclusion

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43 Unbalanced forces cause changes in velocity

44 3 rd law of motion For every action there is an equal and opposite reaction

45 ACTION- REACTION What does this mean? EQUAL and OPPOSITE FORCES Not Ben pushes Matt so Matt pushes back.

46 ACTION- REACTION What does this mean? EQUAL and OPPOSITE FORCES Ben applies a force on the desk and the normal force of the desk applies a force back that is the same size but opposite direction

47 Weight of apple pulling down is 2 N Force of stalk pulling up is 2N

48 Weight of apple pulling down is 2 N Force of stalk pulling up is 1N Apple’s force is bigger than stalk’s force so apple falls and hits Newton on the head

49 The apple falls Apple will apply a force of 10N on Newton’s head Newton’s head pushes back with a force of 10N (hopefully)

50 If the action force is bigger than the reaction force, then one object will accelerate (2 nd law) In this case, the applied force of hammer is 20 N, the normal force of the nail is 5 N so the nail moves.


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