Newton’s Laws

1. Newton’s Laws

2. Newton’s Laws • Newton’s First Law of Motion states that an object at rest (or in motion) will remain at rest (or in motion) unless acted upon by an unbalanced force. • Also known as the law of inertia

3. Newton’s Laws • Newton’s Second Law of Motion states that unbalanced forces cause acceleration. Example #1- 50 N force up, 50 N force down Example #2- 75 N force up, 50 N force down Which example causes acceleration?

4. Case 1-Object at rest FL FL= FR FR If two equal and opposite forces act on an object at the same time, the forces are balanced and the object will remain at rest.

5. Case 2- Object at rest FL FL<FR FR An object at rest has two opposite forces acting on it at the same time. The force to the right is larger than the force to the left. The forces are unbalanced and the object will accelerate to the right.

6. Case 3- Object moving v FL FL= FR FR If an object is moving to the right with equal and opposite forces acting on it, the object will continue moving at constant speed. Therefore, there will NOT be an acceleration.

7. Case 4-Object moving v FL FL<FR FR If an object is moving to the right with two forces acting on it, the greater force to the right, the object will accelerate because the forces are unbalanced (it will speed up).

8. Case 4- Object moving v FL FL>FR FR If an object is moving to the right with two forces acting on it, the greater force to the left, the object will accelerate because the forces are unbalanced (it will slow down).

9. Conclusion Unbalanced forces cause acceleration! Balanced forces do not cause acceleration, the object will either continue to move at constant speed or stay at rest.

10. Newton’s 3rd Law For every action, there is an equal and opposite reaction. Ex: As you sit on your chair, your weight pushes down on the chair while the chair pushes up on you. Ex: When rowing a boat, the oar pushes on the water while the water pushes on the oar.

11. Newton’s Second Law The Equation

12. Newton’s 2nd Law Equation: F= m(a) • F- Force (N-Newton) • m- mass (kg) • a- acceleration (m/s2)

13. Newton’s 2nd Law A special case of Newton’s Second Law is weight. • w = m(g) • w- weight (N) • m- mass (kg) • g- acceleration due to gravity (m/s2) • g = 9.8 m/s2 on Earth

14. Newton’s 2nd Law • Remember that mass is the amount of matter that an object has and is measured in grams or kilograms. • Weight is effected by gravity. It is a type of force measured in Newtons. • g is the acceleration due to gravity. It is not a force.

15. Newton’s 2nd Law • Zookeepers lift a stretcher that holds a sedated lion. The total mass of the lion and stretcher is 175 kg. The upward acceleration of the lion and stretcher is 0.657 m/s2. What is the unbalanced force necessary to produce this acceleration of the lion and the stretcher?

16. Newton’s 2nd Law • F = m (a) • F = 175 kg (0.657 m/s2) • F = 115 N

17. Newton’s 2nd Law • What is the net force necessary for a 1600 kg automobile to accelerate forward at 2 m/s2?

18. Newton’s 2nd Law • F = m(a) • F = 1600 kg (2 m/s2) • F = 3200 N

19. Newton’s 2nd Law • A baseball accelerates downward at 9.8 m/s2. If the gravitational force is the only force acting on the baseball, what is the baseball’s mass for a 1.4 N force?

20. Newton’s 2nd Law • F = m(a) • m = F/a • m = 1.4 N/9.8 m/s2 • m = 0.14 kg

21. Newton’s 2nd Law • A sailboat and its crew have a combined mass of 655 kg. Ignoring frictional forces, if the sailboat experiences a net force of 895 N pushing it forward, what is the sailboat’s acceleration?

22. Newton’s 2nd Law • F = m(a) • a = F/m • a = 895 N/655 kg • a = 1.37 m/s2