Understanding Newton's Laws of Motion: Forces and Acceleration

1. Chapter 3 Forces

2. Section 1 Newton’s Second Law

3. Force, Mass and Acceleration • Compare hard thrown ball vs. gently tossed ball • Force? Velocity? Acceleration? • Throw hard a baseball vs. softball • Who goes faster? Why? • Velocity and Acceleration depend on __________________

4. Newton’s 2nd Law of Motion • Def: _________________________is in the same ________________________ as net force

5. Net Force • Net Force = mass x acceleration Fnet = ______ • kg x m/s2 = _______________________

6. Practice! • Rocket has 28,913 N of thrust and a mass of 2,350 kg. What is the acceleration? (frictionless surface) • What is the mass of a rocket that has a thrust of 105 N and an acceleration of 70 m/s2?

7. Friction • Roll a ball in the parking lot… • Newton’s 1st law says ball will keep ____________________________ • Stops because of friction (negative acceleration – force is __________________) • Def: _________________ that opposes the sliding motion

8. Microwelds • Def: ____________________where two surfaces come in to contact • Larger force = ________________ microwelds • Break microwelds = ______________ force

9. Static Friction • Push box = doesn’t move • Acceleration = ______ so net force = _______ • What’s canceling your force? • ___________________: force prevents two surfaces from sliding past each other

10. Sliding Friction • Def: force that opposes the ________________ motion of two surfaces • Stop pushing = ___________________

11. Rolling Friction • Car stuck in mud… • Def: ________________________________ between rolling object and surface.

12. Air Resistance • Falling object pulled by gravity – ___________________by air resistance • Def: _________________ like force opposed motion as moves through __________ • __________________ = objects fall with same acceleration bowling ball vs. feather

13. Terminal Velocity • Def: ___________________a falling object will reach • When air resistance _________________ downward force • Depends on size, shape, ________________ • Sky diver no parachute vs. with parachute

14. Section 2 Gravity

15. What is gravity? • How would you throw a long pass with a football? • Anything that has mass is attracted by gravity • __________________________: attractive force between two objects that depends on masses and ____________________ • Stronger force? • More mass/closer together

16. Gravity • We only feel ________________ gravitational force • 1 of _______ Basic Forces • Others: • ___________________ force – electricity and magnetism • strong and weak nuclear force – inside nuclei of atoms

17. Law of Universal Gravitation • Sir Isaac Newton

18. Earth’s Gravitational Acceleration • When only force acting on two things is gravity – they fall at the _______________rate • Close to earth’s surface acceleration due to gravity is ______________________ • Newton’s second law  _________________ • Fgravity(N) = mass (kg) x acceleration of gravity (m/s2) • F = mg

19. Weight • Def: ______________________ force on a object • Calculate your weight in N

20. Weightlessness and Free Fall • When you free fall gravity pulls everything at _____________________ = no gravity • Spaceship in orbit experiences ___________ of earth’s gravity • Ship is in free fall in orbit = no gravity

21. Projectile Motion • Projectile: anything ______________ or shot through air • Gravity causes path to be _________________ • Horizontal motion – throwing • Vertical motion – ______________

22. Horizontal and Vertical Distance • Same _____________________ = same mass = same acceleration = same ________________ • Different horizontal distance

23. Centripetal Force • Centripetal acceleration: acceleration towards the ________________ of a curved path. • Newton’s 2nd law – acceleration in direction of force  __________________________ • Anything moving in circle is because cent. force is accelerating towards center

24. Gravity

25. Section 3 Newton’s 3rd Law of Motion

26. Newton’s 3rd Law • Def: when one object exerts a force on another, the 2nd object exerts an ____________ but ________________ force • Action – __________________ • Jumping on trampoline

27. Action/Reaction Do NOT Cancel • Forces are equal, but acting on _______________________ objects • Act on water – reaction pushes forward = unbalanced force

28. Rocket Propulsion • ____________________exerts force on gas backwards – ____________________ exerts force on rocket forwards

29. Momentum • How much force is needed to change motion? • Def: product of ____________________ and velocity

30. Practice! • What is the momentum of a 1,300 kg car traveling 28 m/s? • What is the velocity of a 0.15 kg baseball that has a momentum of 6 kg m/s?

31. Force and Changing Momentum • Catch a foul ball bare handed?

32. Force and Changing Momentum • F = ma a = (vf – vi) t • Put the two together: • When that baseball hits – calculate the force

33. Force and Changing Momentum • What is the force of a 0.15 kg baseball with a velocity of 40 m/s when it comes to a stop in 1 second?

34. Law of Conservation of Momentum • ______________________ doesn’t change unless mass, velocity or both change • Can be _____________________ – pool balls • Def: group of objects exerts forces only on each other, their total momentum doesn’t change

35. When Objects Collide • 1st puck will give more momentum to the 2nd puck in the same direction • Moving towards each other same speed = ___________ momentum • Collide = 0 momentum – moving same speed ________________ direction