Newton’s First Law Notes

Force:• A push or pull

More than one force can act on an object at the same time.

Net Force:• Combination of all forces acting on an object.

Net force means total force.The net force on an object determines how the

motion of an object changes.

Balanced Force Unbalanced Force• two or more forces whose effects cancel each other out and do not change the motion of an object.

• net force is zero

• two or more forces acting on an object that do not cancel, and cause the object to change its motion.

• net force is not zero

Force Diagrams:• Forces are represented by using arrows.

• The larger the arrow the larger the force.

• The smaller the arrow the smaller the force.

1. What is Newton’s first law of motion?• If the net force acting on an object is zero, the

object will remain at rest or move in a straight line with a constant speed.

• An object at rest will stay at rest, an object in motion will stay in motion unless it is acted upon by an unbalanced force.

2. The motion of an object doesn’t change until an unbalanced force acts on it.

Newton’s First Law

Newton’s First Law

Newton’s First Law

Newton’s First Law

Newton’s First Law

Spring Scale

• Measures weight• Unit of measurements:

– Newtons (N)• 1 newton = 100 grams

– Pounds– Kilograms, grams

• Weight is a measure of the force of gravity on an object.

Dates To Remember• Monday, January 9

– Forces Test

• Tuesday, January 10– ALL project grades and improvement to project grades

are done.– Project grades lower than 48 points can be improved.– If you do not see me to grade your project it will be a

zero

• Friday, January 20– Last day of the nine weeks

Review Questions

1. What is a force? Net force?2. Is this object balanced? What is the net

force?

1. What is Newton’s first law of motion?

15 N 10 N

3. What is friction? Give an example.• A force that acts to oppose sliding between

two surfaces that are touching. Examples: air, water, roads, etc.

4. What do different forms of friction have in common?

• Different forms of friction always slow an object down.

5. Is friction a force? Explain.• Yes, it causes moving objects to slow down

and prevents stationary objects from moving if a force is applied to them.

6. In terms of friction and force, how can an object keep moving?

• To keep an object moving, a force has to be applied to overcome the effects of friction.

7. If friction did not exist, describe the motion of any object once an unbalanced force is applied to that object.

• An object in motion would continue to move in a straight line with a constant speed.

Example of Low Friction

Example of Low Friction

Example of Low Friction

8. What are the three types of friction? Describe each.

• Static Friction – surfaces stick together where they are in contact; due to the attraction between the atoms on the two surfaces; no movement by an object.

• Sliding Friction – when a moving object slows down as it slides across an object; due to the roughness of a surface.

• Rolling Friction – when an object rolls across a surface.