NEWTON’S LAWS OF MOTION

A force is a push or a pull that can cause acceleration to happen in an object

We measure forces with the unit know as a NEWTON (which is the force needed to cause a 1 kilogram object ti accelerate at 1m/s2)

A frame of reference is the perspective from which a system is observed.

Whenever you describe something as moving you are comparing it to a frame of reference that is assumed to be stationary.

There are NO truly STATIONARY objects in the universe

- The Nature of Force

The combination of all forces acting on an object is called the net force.

- The Nature of Force

Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion.

- The Nature of Force

Balanced forces acting on an object do not change the object’s motion.

“Things keep on moving the way they are moving" (unless acted upon by an unbalanced force).

Law of Inertia: A body remains at rest or moving in a straight line unless acted upon by some unbalanced force

1. Imagine a place in the cosmos far from all gravitational and frictional influences. Suppose that an astronaut in that place throws a rock.

a The rock willgradually stop.

b. continue in motion in the same direction at constant speed.

Mr. Wegley spends most Sunday afternoons at rest on the sofa, watching pro football games and consuming large quantities of food. What effect (if any) does this practice have upon his inertia? Explain.

Ben Tooclose is being chased through the woods by a bull moose which he was attempting to photograph. The enormous mass of the bull moose is extremely intimidating. Yet, if Ben makes a zigzag pattern through the woods, he will be able to use the large mass of the moose to his own advantage. Explain this in terms of inertia and Newton's first law of motion.

F = ma : A force F applied to a body with mass m will cause it to accelerate (change speed and/or direction) at rate a.

Or the harder the push or pull the greater the acceleration

Force = Mass x AccelerationForce is measured in units called Newtons (N)

A Newton (N) is = to the force needed to make a 1Kilogram object accelerate at 1 meter/second/second

N=Kg m/s2

In elephant-feather scenario, we can say that the elephant experiences a much greater force (which tends to produce large accelerations. Yet, the mass of an object resists acceleration.

Thus, the greater mass of the elephant (which tends to produce small accelerations) offsets the influence of the greater force

It is the force/mass ratio which determines the acceleration

Action and Reaction: Every force (or action) applied, creates a second equal but opposite force (or action) back on the first body.

This law is demonstrated by what happens if we step off a boat onto the bank of a lake: as we move in the direction of the shore, the boat tends to move in the opposite direction (leaving us facedown in the water, if we aren't careful!).

- Friction and Gravity

Two factors affect the gravitational attraction between objects: mass and distance.

- Friction and Gravity

The force of gravity on a person or object at the surface of a planet is known as weight.

Use the graph to answer the following questions.

- Friction and Gravity

◦Time is on the horizontal axis, and speed is on the vertical axis.

Interpreting Graphs:

◦What variable is on the horizontal axis? The vertical axis?

- Friction and Gravity

◦The slope is 9.8. The speed increases by 9.8 m/s each second.

Calculating:

◦Calculate the slope of the graph. What does the slope tell you about the object’s motion?

- Friction and Gravity

◦58.8 m/s

Predicting:

◦What will the speed of the object be at 6 seconds?

- Friction and Gravity

◦The speed values would not change.

Drawing Conclusions:

◦Suppose another object of the same size but with a greater mass was dropped instead. How would the speed values change?

- Friction and Gravity

- Friction and Gravity

Falling objects with a greater surface area experience more air resistance.

G=6.67x10^-11N

R=2GM/speed of light squared

If I have seen further than other men, it is by standing on the shoulders of giants. ◦ ◦ Isaac Newton, Letter to Robert Hooke,

February 5, 1675

I do not know what I may appear to the I do not know what I may appear to the world; but to myself I seem to have been world; but to myself I seem to have been only like a boy playing on the seashore, only like a boy playing on the seashore, and diverting myself, now and then in and diverting myself, now and then in finding a smoother pebble or a prettier finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean shell than ordinary, whilst the great ocean of truth lay all undiscovered before me. of truth lay all undiscovered before me.

Sir Issac Newton–(1643-1727)Sir Issac Newton–(1643-1727)

(1) Speed=Distance/time(2) Distance = Speed x time(3) Time = distance/speed(4) Accel = (Vf –Vi)/time

If Force=Mass x acceleration (5) F=ma Then (6) F/m=acceleration And (7)F/a=mass