Download presentation

Published byDiane Henderson Modified over 4 years ago

1
**Newton’s First Law Mathematical Statement of Newton’s 1st Law:**

If v = constant, ∑F = 0 OR if v ≠ constant, ∑F ≠ 0

2
Mass (Inertia) Inertia The tendency of a body to maintain its state of rest or motion. MASS: Property of an object that specifies how much resistance an object exhibits to changes in it’s velocity. A measure of the inertia of a body Quantity of matter in a body A scalar quantity Quantify mass by having a standard mass = Standard Kilogram (kg) (Similar to standards for length & time). SI Unit of Mass = Kilogram (kg) cgs unit = gram (g) = 10-3 kg Weight: (NOT the same as mass!) The force of gravity on an object.

3
**Newton’s Second Law (Lab)**

1st Law: If no net force acts, object remains at rest or in uniform motion in straight line. What if a net force acts? Do Experiments. Find, if the net force ∑F 0 The velocity v changes (in magnitude or direction or both). A change in the velocity v (dv) There is an acceleration a = (dv/dt) OR A net force acting on an object produces an acceleration! ∑F 0 a

4
Newton’s 2nd Law Experiment: The net force ∑F on an object & the acceleration a of that object are related. HOW? Answer by EXPERIMENTS! Thousands of experiments over hundreds of years find (object of mass m) : a (∑F)/m (proportionality) Choose the units of force so that this is not just a proportionality but an equation: a (∑F)/m OR: (total force!) ∑F = ma

5
**∑F = ma Newton’s 2nd Law: ∑F = ma**

∑F = the net (TOTAL!) force acting on mass m m = the mass (inertia) of the object. a = acceleration of the object. Description of the effect of ∑F. ∑F is the cause of a. ∑F = ma The Vector Sum of All Forces Acting on Mass m!

6
**FUNDAMENTAL & IMPORTANT LAWS OF CLASSICAL PHYSICS!!!**

Based on experiment! Not derivable mathematically!! Newton’s 2nd Law: ∑F = ma A VECTOR equation!! Holds component by component. ∑Fx = max, ∑Fy = may, ∑Fz = maz ONE OF THE MOST FUNDAMENTAL & IMPORTANT LAWS OF CLASSICAL PHYSICS!!!

7
**2nd Law Force = an action capable of accelerating an object.**

Units of force: SI unit = the Newton (N) ∑F = ma , units = kg m/s2 1N = 1 kg m/s2

8
**Example 5.1: Accelerating Hockey Puck**

See Figure: A hockey puck, mass m = 0.3 kg, slides on the horizontal, frictionless surface of an ice rink. Two hockey sticks strike the puck simultaneously, exerting forces F1 & F2 on it. Calculate the magnitude & direction of the acceleration. Steps to Solve the Problem 1. Sketch the force diagram (“Free Body Diagram”). 2. Choose a coordinate system. 3. Resolve Forces (find components) along x & y axes. 4. Write Newton’s 2nd Law equations x & y directions. 5. Use Newton’s 2nd Law equations & algebra to solve for unknowns in the problem. x & y directions.

9
Example

10
**Sect. 5.5: Gravitational Force & Weight**

Weight Force of gravity on an object. Varies (slightly) from location to location because g varies. Write as Fg mg. (Read discussion of difference between inertial mass & gravitational mass). Consider an object in free fall. Newton’s 2nd Law: ∑F = ma If no other forces are acting, only Fg mg acts (in vertical direction) ∑Fy = may or Fg = mg (down, of course) SI Units: Newtons (just like any force!). g = 9.8 m/s2 If m = 1 kg, Fg = 9.8 N

11
Newton’s 3rd Law 2nd Law: A quantitative description of how forces affect motion. BUT: Where do forces come from? EXPERIMENTS Find: Forces applied to an object are ALWAYS applied by another object. Newton’s 3rd Law: “Whenever one object exerts a force F12 on a second object, the second object exerts an equal and opposite force -F12 on the first object.” Law of Action-Reaction: “Every action has an equal & opposite reaction”. (Action-reaction forces act on DIFFERENT objects!)

12
**Another Statement of Newton’s 3rd Law**

“If two objects interact, the force F12 exerted by object 1 on object 2 is equal in magnitude & opposite in direction to the force F21 exerted by object 2 on object 1.” As in figure

13
**Example: Newton’s 3rd Law**

14
**Action-Reaction Pairs: On Different Bodies**

Similar presentations

© 2019 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google