- review the law of interaction and balanced forces within bodies with constant motion - observe and...
TRANSCRIPT
- Review the Law of Interaction and balanced forces within bodies with constant motion
- Observe and plot an example of acceleration of an object
- Study the effects of a change in velocity on an object
TODAY’S OUTCOMES:FORCE, MOTION AND ENERGY
Weight of the cantaloupe ↓Force of the scale hook on the cantaloupe ↑Force pulling on the scale spring ↓Scale spring pulling upward ↑Scale + cantaloupe pulling on hand ↓Hand pulling back on scale + cantaloupe ↑
If the scale has no weight, all these forces are equal in strength, and exist in pairs in opposing directions.
14. Hannah is weighing a cantaloupe using a weightless scale. There are many forces acting, as indicated by the diagram.
A. Some of these forces are related to others by the Law of Interaction. List these relationships (please give the full name of each force).
B. Some of these forces are related to others by the Law of Inertia. List these relationships.
Law of Interaction (often called Newton's Third Law): “For any two objects A and B, the force of A on B is equal and opposite to the force of B on A.”
The Law of Inertia (Newton’s First Law): In the absence of external forces, an object moves in a straight line with constant speed. In this case, the speed is 0 !
No part of the hand-scale-cantaloupe structure is changing its speed, so the forces acting on it must all cancel out in pairs, as listed above.
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equal and opposite pair
equal and opposite pair
equal and opposite pair
Weight of the cantaloupe ↓Force of the scale hook on the cantaloupe ↑Force pulling on the scale spring ↓Scale spring pulling upward ↑Scale + cantaloupe pulling on hand ↓Hand pulling back on scale + cantaloupe ↑
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equal and opposite pair
equal and opposite pair
equal and opposite pair
C. Suppose the scale has weight (this force is not indicated on the diagram). How does this change any of the answers to parts A and B?
If the scale has weight, then one pair of the above forces (shown in red)will be greater than the others - but this pair is STILL equal and opposite, and will not affect the measurement on the scale.
In your lab, you pulled a cart at a constant speed up a hill
What forces were acting on the cart?
How did these forces compare?
The scale pulled the cart UP the hill.Gravity & contact against the wheels pulled the cart back DOWN the hill.
If the cart moves at a constant speed, these forces MUST be equaland opposite.
In your lab, you pulled a cart at a constant speed up a hill
What forces were acting on the cart?
How did these forces compare?
The table pushes upward on the cart wheels.
Gravity pulls the cart downward.
They are equal and opposite.
What if the cart is just sitting on the table?
The sum of both scale measurements totalledabout 2 Newtons.
You also held a 200 gram mass with 2 springscales.
If held directly above the mass, what wasthe (approximate) total force measured on the scales?
What forces operate in this diagram?2 Newton weight of the 200 gram mass pulling on the rubber bands
Forces totalling 2 N. at the bottoms of the rubber bandsRubber bands pulling on the bottoms of the hooks (totalling 2 N.)Springs in the scales pulling upward (2 N. total)Also a pair of opposing forces between handsand the scale (not shown)
What do all these examples have IN COMMON?
CONSTANT SPEED AND DIRECTION(zero speed is also a constant speed!)The Law of Inertia (Newton’s First Law): In the absence of external forces, an object moves in a straight line with constant speed.
Law of Interaction (often called Newton's Third Law): “For any two objects A and B, the force of A on B is equal and opposite to the force of B on A.”
What are “external forces” ? Keep this question in mind during today’s activity!
This is always true! Always think - when you observe a force, where is the equal and opposite force?
- The meaning of the Law of Interaction (Newton’s Third Law), and how forces exist in pairs
- That the Law of Inertia demands all forces mustcancel within an object with a constant speed and direction
WHAT YOU ARE EXPECTED TO KNOW:
- Review the Law of Interaction and balanced forces within bodies with constant motion✓
- Observe and plot an example of acceleration of an object
- Study the effects of a change in velocity on an object
TODAY’S OUTCOMES:FORCE, MOTION AND ENERGY