 # I. FORCES.

## Presentation on theme: "I. FORCES."— Presentation transcript:

I. FORCES

1. What is a force? A lift, push or pull

2. What is a net force? The combination of all the forces acting on an object Determines whether the velocity of the object will change An object accelerates in the direction of the net force An object will not accelerate if the net force is zero

What are the net forces acting on the following?

3. What are balanced forces?
Forces that are equal in size and opposite in direction They combine to produce a net force of zero No change in motion occurs (no acceleration)

4. What are unbalanced forces?
Forces that are unequal They cause a change in motion (acceleration) Ex: tug of war

5. How are forces shown? Using arrows
The length of the arrow represents the strength of the force The direction of the arrow represents the direction of the force

Identify whether balanced or unbalanced forces are responsible for the following different types of movement. A discus thrown through the air. A gymnast balanced on a beam. A sprinter running a bend at a constant speed in a 200 m race. A vehicle traveling along a horizontal linear air track A car that has a deceleration of 9 m/s2 A lift traveling downwards at a constant speed of 1m/s.

6. What is friction? A force between two objects in contact that opposes the motion of the objects It will cause a moving object to slow down and eventually stop Friction between rough surfaces is greater than friction between smooth surfaces Friction is not always bad – some times we need friction (Ex: to walk, to stop a car)

7. What is air resistance? A form of friction caused by air hitting against the surface of a moving object

8. What is gravity? The attraction between two particles of matter due to their mass Gravity is a force

9. What is the law of gravitation?
It states that all objects in the universe attract each other by the force of gravity The size of this force of gravity depends on 2 things: The masses of the objects (gravity increases as the masses increases) The distance between the objects (gravity decreases as the distance between the objects increases)

II. NEWTON’S LAWS OF MOTION

1. Who is Isaac Newton? The founder of modern physics

2. What is Newton’s 1st law of motion?
An object at rest remains at rest and an object in motion remains in motion at a constant velocity unless acted upon by an unbalanced force

3. What are some examples of Newton’s 1st law of motion?
Riding in a car and slam on brakes and you continue forward

4. What is inertia? The tendency of an object to remain at rest or in motion with a constant velocity All objects have inertia because they resist changes in motion

5. What is Newton’s 2nd law of motion?
An unbalanced force acting on an object equals the object’s mass times its acceleration. It describes the effect of unbalanced forces acting on an object The greater the force, the greater the acceleration if the mass remains constant The greater the mass, the greater the force needed to accelerate an object

6. What is the formula for Newton’s 2nd law of motion?
Force = mass x acceleration or F = ma

7. What are some examples of Newton’s 2nd law of motion?
Pushing an empty grocery cart vs. pushing a full grocery cart

8. What unit is used to measure force?
Newton

10. What is weight? A measure of the force of gravity on an object

11. How can F = ma be used to calculate your weight?
Weight = mass x gravitational acceleration W = mg

12. How are weight and mass different?
Mass is a measure of the amount of matter in an object Weight is a measure of the gravitational force an object experiences due to its mass (so weight depends on gravity) An object’s weight changes when gravity changes but mass always stays the same.

14. What is Newton’s 3rd law of motion?
(law of action and reaction) for every action force, there is an equal and opposite reaction force Forces always occur in pairs The action/reaction forces act on different objects

15. What are some examples of Newton’s 3rd law of motion?
rocketry

17. What are 3 types of frictional forces?
Sliding friction – occurs when a solid surface slides over another solid surface Rolling friction – occurs when an object rolls across a solid surface (rolling friction tends to be less than sliding friction) Static friction – occurs between the surfaces of two objects that touch but do not move against each other. To move an object, static friction must be overcome.

18. What is a net force? The combination of all the forces acting on an object If the net force is zero, no change in movement occurs.

The correct answer is A. To determine the net force, you must subtract the two forces since they are in opposite directions: 20 N – 20 N = 0 N.