Physics BasicsPhysics Basics

TAKS Objective FourTAKS Objective Four

TAKS Objective 4 – The student will demonstrate an understanding of motion, forces, and energy.

Learning Objectives During this Unit

Learning Objectives During this Unit

• You will apply the laws of motion to real world examples.

• You will identify size and direction of a force.

• You will determine if motion is constant or accelerated.

Learning ObjectivesLearning Objectives

• You will use equipment to measure time and distance so that the motion of the object can be determined.

• You will used data collected to calculate the speed of an object.

• You will explain the results of applying a force to an object.

True or FalseTrue or False

• Speed is the same as velocity.

• False.

True or FalseTrue or False

• The acceleration of an object does NOT depend on its mass.

• False.

True or FalseTrue or False

• An ice skater uses projectile motion.

• False

Types of MotionTypes of Motion

• One dimensional motion happens when only one directional force causes an object to move forward, backward, up and down, or side to side.

• Examples: bowling, skiing, writing, brushing your teeth, painting a wall

Projectile MotionProjectile MotionConsider two-dimensional motion:

A horizontal motion that follows Newton’s First Law.

A vertical motion due to the force of gravity pulling the ball back to Earth. This is an acceleration motion. It is acted upon by the constant force of gravity and follows Newton’s Second Law (F = ma).

Example of Projectile MotionExample of Projectile Motion

Newton’s First LawNewton’s First Law

• An object at rest will remain at rest and an object in motion will remain in motion in a straight line until a force opposes it.

Newton’s Second LawNewton’s Second Law

• The acceleration of an object depends on the force applied to the object and the mass of the object. F = ma

DefinitionsDefinitions

• Force – A force is an interaction with an object which may or may not result in motion.– Person sitting in chair– Pushing on a wall– Blowing a feather– Kicking a ball

Two types of forcesTwo types of forces

• Contact Force – normal, frictional,

tensional, and applied forces

• Action-at-a-distance interaction forces– gravitational, electrical,

and magnetic forces

Force Unit definedForce Unit defined

• One Newton is defined as the amount of force required to give a 1-kg mass an acceleration of 1 m/s2.

• What acceleration will result when a 12-N net force is applied to a 3-kg object? A 6-kg object?

• 4m/s2 and 2m/s2

F = maF = ma

• A net force of 16 N causes a mass to accelerate at the rate of 5 m/s2. Determine the mass.

• Write what you know…. 16 = m5

• 3.2 kg

Newton’s Third LawNewton’s Third Law

• For every action there is an equal in size and opposite in direction action.

Forces always come in pairs – equal and opposite action-reaction force pairs.

DefinitionsDefinitions

• Speed – describes an object’s change in position over time – Speed = Distance / Time

DefinitionsDefinitions

• Velocity – the speed AND direction of an object. Velocity= Distance / Time plus direction. Example: 3 m/s eastward

DefinitionsDefinitions

• Acceleration – a change in either the speed or the direction of an object. A = Force / Mass

• Which car(s) is/are accelerating?

Which letter represents which car?

Which letter represents which car?

DefinitionsDefinitions

• Work – force acting upon an object multiplied by the distance the object moves. (force and displacement must move in the same direction. W = F X D

• Power – The amount of time it takes to do work. Power = Work / Time

Is this work or not?Is this work or not?

• A teacher applies a force to a wall and becomes exhausted.

• No, the wall did not move in the same direction as the force.

• A book falls off a table and free falls to the ground.

• Yes, gravity pulls the book downward.

Is this work or not?Is this work or not?

• A waiter carries a tray full of meals above his head by one arm across the room.

• No, his tray is moving horizontally while he is applying a vertical force.

• A rocket accelerates through space.• No, the rocket engine propels the rocket in

the opposite direction it goes.

• Joule is the unit used for work

Study theseStudy these

• Newtons Laws of Motion

• Force• Acceleration• Velocity• Speed• Work• Joule• Newton

• Projectile Motion• Power• Know how

acceleration is affected by mass and amount of force

• Get some objects out while you study to help you understand what you are learning.