Newton’s Laws of Motion
- Historical Perspective
- Observer not an experimenter
- A force has to act on an object for it to move
- Velocity was proportional to that force
- supported heliocentric model of the earth
- no force is required to maintain motion once it is initiated
- included acceleration in his theories
- Isaac Newton
- Proposed a theiry of the causes of motion that could explain the motion of ANY object
- Three laws of motion and the law of universal gravitation
- Could confirm predictions using these laws
- Newton’s Laws of Motion
- Newton’s first law of motion
- explains what happens in the absence of force
- An object remains at rest, or in uniform motion in a straight line, unless it is compelled to change by an externally imposed force.
- The velocity will not change unless a force acts upon the object (constant velocity)
If F = 0
v = 0 (at rest) remain at rest
v v v v
- Why do things that are moving stop?
- Newton’s second law of motion
- Explains the effects of applying a force to an object
- The central idea of his theory of motion
- The acceleration of an object is directly proportional to the magnitude of the imposed force and inversely proportional to the mass of the object.
- The acceleration is in the same direction as that of the imposed force.
Acceleration is proportional to force
Acceleration is inversely proportional to mass
- Second Law is the central idea of Newton's theory of motion
- Total force => the imposed force in the NET force.
( 1N = 1 kgm/s2)
F1 = 10 N
F2 = 2N
- Total force acting on the block?
FT = F1 + (- F2)
FT = 10N + (- 2N) = 8N
- Acceleration of the block?
F = ma
a = F/m
a = 8N/5kg
a = 1.6 m/s2
- Mass and Weight
- Mass (kg) => The property of matter that determines its resistance to a change in motion. The measure of an objects inertia.
- Weight (N) => A measurement of the gravitational force acting on an object.
- How are mass and weight related?
- Why is gravitational acceleration independent of mass?
- Therefore, gravitational force is proportional to mass but acceleration is inversely proportional to mass.
- Newton’s third law of motion
- action/reaction principle
- For every action there is an equal and opposite reaction
- Force comes from interaction with other objects
- How to identify the different forces
- The forces that cause a car to accelerate
- Applications of Newtons Laws
- Newton’s law of universal gravitation
- The gravitational force between two objects is proportional to the mass of each object and inversely proportional to the square of the distance between the centers of the masses.
F = r2
Mass 1 Mass 2