Standards S8P3. Obtain, evaluate, and communicate information about cause and effect relationships between force, mass, and the motion of objects. Construct an explanation using Newton’s Laws of Motion to describe the effects of balanced and unbalanced forces on the motion of an object. c. Construct an argument from evidence to support the claim that heavier objects require a greater force to accelerate (inertia).

Phenomena https://www.youtube.com/watch?v=9a22EsWs9Gk

Essential Questions? What is force and motion? What is the first law of motion? What is gravity and how does it affect the motion of an object? What is friction and how does it affect the motion of an object? What is mass and how does it affect the motion of an object?

What makes objects change speed or direction? FORCES

What is a Force? Definition: A force is a push or pull that causes an object to move, stop, or change direction In physics, a force is anything that makes an object accelerate

What is a Force? The student is pushing down on the chair, but the chair does not move. The floor is balancing the force by pushing on the chair.

What is a Force? In science, a force is a push or a pull. All forces have two properties: Direction and Size A newton (N) is the unit that describes the size of a force.

Newtons? Sir Isaac Newton? Yes! The unit for measuring force is NEWTON(S). It is named for that famous scientist!

Friction! There are four main types of friction: Sliding friction: ice skating Rolling friction: bowling Fluid friction (air or liquid): air or water resistance Static friction: initial friction when moving an object

Friction – force that slows or prevents motion 1. Sources a. roughness of surface; ex. road, floor b. Weight (forces pushing surfaces together); large object has more friction

2. Types a. static friction – friction at rest; ex. eraser sits still b. sliding friction – something pushed across a surface; ex. box pushed on floor

c. rolling friction – between wheels & floor; ex. car d. fluid friction – friction of liquids or gases; ex. airplane, boat

3. reducing friction a. lubricants – oil, wax, grease b. switch from sliding to rolling c. smooth surface – ex. use sandpaper

4. increasing friction – make surfaces rougher & increase the weight (forces pushing the surfaces together

Forces in the Same Direction When forces are applied in the same direction, they are added to determine the size of the net force.

Forces in Different Directions When two forces act in opposite directions, you subtract the smaller force from the larger force to determine the net force. The net force will be in the same direction as the larger force.

Balanced & Unbalanced Forces

Balanced Force When the forces on an object produce a net force of 0 N, the forces are balanced. There is no change in the motion of the object.

Balanced Forces They are equal in size and opposite in direction

Balanced Forces (Balanced Forces = No Acceleration) Object 5 N 5 N Notice that all the forces are equally pointed in the opposite direction. Hence they balance each other – or cancel each other. Equal Pushing Forces may cancel each other and produce No Acceleration!

Balanced Forces Balanced Push No Acceleration i.e. Pushing a Car Pull i.e. Tug-o-war 10N 10N 10N 10N

Balanced Forces (Balanced Forces = No Acceleration) Ground pushes up Gravity pulls down Gravity pulls down on you… The ground pushes back up… THIS KEEPS YOU WHERE YOU ARE! If these football players push on each other equally as hard, will either one move?

Unbalanced Force When the net force on an object is not 0 N, the forces on the object are unbalanced. Unbalanced forces produce a change in motion of an object.

Unbalanced Forces Causes Acceleration Adding Forces Object 5 N 5 N Notice that all the forces are pointed in the same direction. Hence they add together.

Unbalanced Forces Causes Acceleration Subtracting Forces Object 5 N 5 N 5 N Notice that all the forces are unequal and pointed in the opposite direction. Hence they are unbalanced and in opposition to each other – or one partially cancels the other.

Unbalanced Forces Causes Acceleration Adding Forces Subtracting Forces

Un-Balanced Forces Additive Un-Balanced Faster Same Direction Acceleration Subtractive Opposite Direction Slower 10N 10N 10N 10N 10N

Subtracting Forces 10 N = 5 N 5 N Two forces can subtract to produce a net force in the direction of the larger force. Negative Acceleration occurs (Slow Down)

Balanced v. Unbalanced Forces If all forces are balanced there is no acceleration in any direction. (Either Zero Motion or Constant Velocity) If one force is greater than the opposing force we get acceleration in a direction.

Are these Balanced or Unbalanced Forces?

Newton’s 1ST Law of Motion Ex. This law explains why you fly forward in a car when someone slams on the brakes. Because of Inertia, your body wants to keep moving at the same speed as the car. 1st Laws States that an object at rest will remain at rest and an object in motion will remain in motion, unless an outside force acts on it (such as friction). This law is also called the LAW OF INERTIA.

Newton’s 2nd Law of Motion 2nd Law States that a force on an object will move the object in the direction of the force. The relationship between force, mass and acceleration is summarized by the formula: f = ma Ex. This law explains why a golf ball will roll in the direction of a force applied to it.

Q: The frog leaps from its resting position at the lake’s bank onto a lily pad. If the frog has a mass of 0.5 kg and the acceleration of the leap is 3 m/s2, what is the force the frog exerts on the lake’s bank when leaping? A) 0.2 N (B) 0.8 N (C) 1.5 N (D) 6.0 N

Newton’s 3rd Law of Motion 3rd Law States that for every action there is an equal but opposite action. Ex. A skater pushes back on the skates but the skater moves forward. THESE LAWS EXPLAIN ALL MOTION

Question The hands of a swimmer pushing backward against water represent an action force. What is the reaction force? A. The swimmer’s body moving forward? B. The water pushing against the swimmer’s hands C. The swimmer’s body pushing against the water. D. The water moving backward from the swimmer.

Friction A force that opposes, or works against, motion of two objects that are touching.

Friction causes an object to slow down and stop. Since the amount of energy stays constant, the energy becomes heat. Air resistance is an another example of friction. Lubricants or grease reduce friction.

Universal Law of Gravity All objects in the universe attract each other by the force of gravity.

Universal Law of Gravity Gravity varies depending on two factors: 1) the mass of the object doing the pulling, and 2) the distance from the center of that object

On Earth gravity = 9.8 m/s/s For every second that an object falls its speed increases by 9.8 m/s

Vocabulary Inertia: the tendency of an object to resist changes in its state of motion Acceleration: •a change in velocity •a measurement of how quickly an object is changing speed, direction or both Velocity: The rate of change of a position along a straight line with respect to time Force: strength or energy