Gravity and Motion Chapter 2 Section 1

Which Will Hit The Ground First? Watch the video and answer the questions on the notes worksheet.

Gravity and Acceleration All objects fall at the same rate. Why? – Acceleration is related to mass and force (gravity). – Gravitational force is smaller on lighter objects and greater on heavier objects. – The mass and gravitational force balance out so that the effect is the same on all objects no matter what their mass is causing them to hit the ground at the same time.

Acceleration Due to Gravity Remember-Acceleration is the rate velocity (speed with a direction) changes over time. Due to the force of gravity all objects accelerate at a rate of 9.8 m/s 2 on earth. What does this mean? That every second and object falls toward earth it’s velocity increases 9.8 m/s down.  v (change in velocity) = g (gravity) X t (time)

A penny at rest is dropped from the top of a tall stairwell. What is the penny’s velocity after it has fallen for 2 s?  v = g x t V= (9.8 m/s 2 ) x (2 s) V = 19.6 m/s

Clearing Up any Misconceptions 68LyZM 68LyZM

Air Resistance Air resistance causes a falling object’s acceleration to slow down. The amount of air resistance experienced by a falling object depends on it size, shape and speed of the object. Thinking about a piece of paper, how can you reduce the amount of air resistance affecting it as it falls? Why? Terminal Velocity occurs when the air resistance and the gravitational force are equal and there is no net force.

Free Fall A free fall occurs when the only force affecting a falling object is gravity. This only occurs in locations without air resistance which means there is no air. This occurs in space and in a vacuum. Astronauts are not truly weightless in space. They are really free falling. NNLQ NNLQ

Orbiting Two forces keep an object in orbit- gravity and centripetal force. Centripetal force is the force that keep an object moving in a circular path. The moon remains in orbit because the gravity of earth attracts the moon and the centripetal force of the moon keeps the moon at its current distance from earth. QJw QJw

Projectile Motion When you throw a ball, what shape does the ball take as it travels through the air? Watch this video clip to see if your response was correct.

Projectile Motion Curved path an object follows when thrown near the surface of the earth. Two components make up the motion – Horizontal It is the force received by the object from whatever is causing it to be thrown. The motion is parallel to the ground – Vertical It caused by the force of gravity pulling the object toward the earth. The motion is perpendicular to the ground The two motions cause the object to travel in a curved path.

Summary Gravity causes objects to accelerate at a rate of 9.8 m/s 2. Air resistance slows a falling object down because it applies a force in the opposite direction of the motion of the object. Free fall causes objects to feel weightless and only occur in places where gravity is the only force acting on it. Objects remain in circular motion because of centripetal force. Projectile Motion occurs when an object is thrown near the earth’s surface. The reason the object moves in a curved path is due to horizontal and vertical motion.