Force and Motion

Physical Science

Forces and Motion

Forces can create changes in motion (acceleration or deceleration).

Definition of a Force

A force is a push or a pull.

Balanced Force

A force that produces no change in an object’s motion because it is balanced by an equal yet opposite force.

Unbalanced Forces

Are forces that result in an object’s motion being changed.

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Motion can be described as:

A change in an object’s position.

Newton’s 1ST Law of Motion

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.

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.

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.

(A) 0.2 N(B) 0.8 N(C) 1.5 N(D) 6.0 N

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?

Formula chart says F=ma, m is mass in kg, a is acceleration in m/s2.

So, .5 kg x 3 m/s2= 1.5 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

Q: 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

handsC. 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

• Friction causes an object to slow down and stop.

• Since the amount of energy stays constant, the energy becomes heat.

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