Newton’s 1 st Law Inertia. Force Anything capable of changing an object’s state of motion Any...
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Transcript of Newton’s 1 st Law Inertia. Force Anything capable of changing an object’s state of motion Any...
Newton’s 1st Law
Inertia
Force
Anything capable of changing an object’s state of motion
Any push or pull Causes object to speed up, slow down, or
change direction (acceleration)
Galileo’s Experiment
Inertia
Galileo reasoned without friction ball would keep going
Also reasoned that ball initially at rest would stay that way unless something caused it to move
Inertia - what Galileo called the tendency of an object to maintain its initial state
Law of Inertia
Object at rest will remain at rest or object in motion will remain in uniform motion in a straight line
Newton
Related mass to inertia More massive objects resist change more Newton’s 1st Law – in the absence of an
unbalanced force, a body at rest remains at rest and a body in motion with a constant velocity
Force(s) acting must be external and must not total zero
Summary
Newton’s 2nd Law
Free Body Diagram
Used to show all net forces acting on an object What can an object with a net force of zero be
doing? Draw the free body diagram for a box being
acted on by all the following forces: 5N (W), 3N(S), 8N (N), and 7N(E)
Can it be at rest? Can it be at a constant speed? What is it doing?
Force on Object
Objects acted on by a net unbalanced force will accelerate in the direction of the force
This means they will speed up, slow down, or change direction
Newton’s 2nd Law
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to the mass.
The direction of acceleration is the same as the direction of the force
a = ∑F / m
∑F = ma
Force Redefined
Force can be redefined as an action capable of accelerating an object
Unit of force is the Newton (N) One Newton is the force needed to
accelerate a 1 kg mass at 1 m/s2
1 N = 1 kg m/s2
Examples
What force is needed to accelerate a 1000kg car at ½ g?
What is the net force required to bring a 1500 kg car to rest from 100 km/hr within a distance of 55 m?
A 50 kg go-cart starts from rest and is accelerated by a 550 N force. If the cart experiences a 280 N friction force and 35 N of air resistance, find
a) it’s acceleration
b) it’s velocity after 3.0 s
c) its displacement after 3.0 s
What force must be exerted on a 500 kg crate in order to move it from rest to 3.0 m/s in 1.0 s?