1. Physics 213 General Physics Chapter 5

2. Laws of Physics

3. True or False? All things in nature obey the laws of physics Most things in nature obey the laws of physics Some things in nature obey the laws of physics

4. Laws of Physics Man-made Based on our observation of God’s creation

5. Newton’s 1 st Law Objects at rest tend to remain at rest unless acted upon by an external force Objects in motion tend to remain in motion unless acted upon by an external force

6. Newton’s 1 st Law Simply put; objects tend to resist changes in their state of motion Putting it another way, objects tend to resist acceleration This tendency to resist changes in their motion is called inertia

7. Force A force is required to cause a change in motion

8. Force A force is required to cause an change in motion acceleration

9. Force A force is required to cause an change in motion acceleration Newton’s 1 st Law

10. Types of Forces: Gravitational Electrical Magnetic Normal (support) Friction Tension Elastic (spring force)

11. Newton’s 2 nd Law Newton observed that if a force is exerted on an object, the object accelerates By measuring displacements and times, he was able to calculate the corresponding acceleration

12. Newton’s 2 nd Law F → a

13. Newton’s 2 nd Law Newton observed that an increase in force results in an increase in acceleration Likewise a decrease in force results in a decrease in acceleration The acceleration is directly proportional to the force causing the acceleration By changing the magnitude of the force applied to the same object, the acceleration changed proportionally

14. Newton’s 2 nd Law

15. How do you turn the ≈ into = ?

16. Newton’s 2 nd Law How do you turn the ≈ into = ? How do you turn the proportionality into an equation?

17. Newton’s 2 nd Law

20. Examples 1, 2, 3

21. Newton’s 3 rd Law When an object exerts a force on a second object, the second object exerts an equal and opposite force on the first object If I push on the wall with a force of 10 lbs, the wall pushes back on me with a force of 10 lbs

22. Newton’s 3 rd Law What force causes an automobile to move? What force causes a propeller-driven airplane to move? What force causes a rowboat to move? What force causes you to move when you walk? If a small sports car collides head-on with a massive truck, which vehicle experiences the greater impact force? Which vehicle experiences the greater acceleration due to the impact?

23. Newton’s 3 rd Law When a car collides with a mosquito, both feel the same force. Why does the mosquito stop while the car continues, seemingly unaffected?

24. Summary of Newton’s Laws 1 st Objects tend to resist changes in motion 2 nd An object’s acceleration is proportional to the net force applied to it 3 rd Every force has an equal and opposite force