Physics
Free Falling Object
A free falling object is an object that is falling under the sole influence of gravity, with no other forces acting upon it. In this state, the object experiences a constant acceleration due to gravity, typically denoted as 9.81 m/s^2 near the surface of the Earth. The motion of a free falling object can be described using equations of motion derived from Newton's laws of motion.
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4 Key excerpts on "Free Falling Object"
- eBook - ePub
The Really Useful Science Book
A Framework of Knowledge for Primary Teachers
- Steve Farrow, Amy Strachan(Authors)
- 2017(Publication Date)
- Routledge(Publisher)
Contrary to the belief of Aristotle (Greek philosopher and scientist), Galileo (Italian scientist) proved that, in the absence of air resistance, all objects fall to the ground at the same rate. He tested this by dropping two balls, one light and the other heavy, to show they both hit the ground at the same time. This was further proved by astronauts on the Moon, who dropped a feather and hammer, simultaneously, that touched the surface at the same time.An object falling through the Earth’s atmosphere will not continue to accelerate indefinitely. At some stage, the force of air resistance, or drag, will equal the weight of the falling object. At this point, the forces on the object will balance, the object will stop accelerating and it will continue to fall at a constant speed, known as its terminal velocity. As an example, the terminal velocity of free-fall parachutists is about 120 mph (193 kph).WORKING SCIENTIFICALLY
Paper helicopters
Children can investigate the factors affecting air resistance on paper helicopters. By changing the weight (adding paper clips), the size of the body or wings, or the shape of the wings, they can time how long it takes the spinner to land.
The third law of motion states that every action has an equal and opposite reaction.The third law of motionImagine a 1-kg mass placed on a table. Because of the acceleration due to gravity, the 1-kg mass is exerting a downward force of 9.8 N on the table. The table is solid and rigid and is not moved by the force of the mass pushing down on it. Instead, it provides a reaction or contact force, exactly equal and opposite to the force applied by the 1-kg mass, and this reaction force supports the mass in a stationary position on the table surface. It is conventional, as in Figure 4.21 , to represent the size and direction of the forces concerned by arrows of appropriate length and direction. The forces in this instance constitute a balanced pair, and the 1-kg mass remains stationary.This is a difficult concept. Some accounts describe the table in the first example as ‘pushing back’ on the 1-kg mass, and many people find it hard to accept that the table actively ‘pushes’ the mass with exactly enough force to keep it in position. An easier concept, in my opinion, is the idea that the force provided by the 1-kg mass produces an equal and opposite reaction force on contact that supports - Paul Grimshaw, Neil Fowler, Adrian Lees, Adrian Burden(Authors)
- 2007(Publication Date)
- Routledge(Publisher)
The pages of this book and the person who is reading it will be exerting an attractive force on each other. However, because of the relatively small masses involved (i.e., the pages of the book and the human body) the force will be very small and it will not be possible to observe its effects. The planet Earth (due to its very large mass) exerts a significant force on the human body. This force produces the weight of an individual or object. The attractive force of the Moon on your body is less than the attractive force you experience on the planet Earth (because the Moon has much less mass than the Earth). Hence you will weigh less on the Moon although your mass will be exactly the same. This is the reason that astronauts are able to jump large distances when they are on the surface of the Moon. The force of gravity is an external force that acts on all bodies.The force of gravity is constantly acting on all bodies. The effect of the force of gravity (in the balance of all external forces that are acting, i.e., the net force) results in an acceleration of the body or object. The acceleration on the planet Earth is given as –9.81 m/s2 (presented as a minus value because the force of gravity from the Earth acting on the body will be trying to pull the body downward toward the center of mass of the Earth).Acceleration caused by the force of gravityOn the planet Earth the effects of the force of gravity due to the mass of the planet act on all objects that have mass. However, this effect will only act on the vertical component of any movement. Any horizontal component of movement will be independent of the external force of gravity. For objects that are at or close to the surface of the Earth the acceleration of –9.81 m/s2 is considered to be constant. This acceleration (because of the position of the object in relation to the center of the Earth and because of the Earth’s relative large mass compared to the object’s small mass) will act on all objects with the same rate regardless of their mass. Hence, dropping a hammer and a pen from the same height while on or at the surface of the Earth will result in both objects hitting the floor at the same time (neglecting air resistance).Air resistanceIn some situations, within human movement and sport, the effects of air resistance (as an external force) are not- eBook - ePub
- Colin Salter(Author)
- 2021(Publication Date)
- Pavilion(Publisher)
The story that he demonstrated this by dropping objects from the top of the leaning Tower of Pisa is probably a myth – he makes no reference to it in his notes. He released balls at the top of an inclined plane to slow their speed uniformly and make it easier to measure accurately.Aristotle thought that inertia was the natural state and believed that any moving object would eventually stop moving once the force that had propelled it stopped. Galileo recognized that what stops movement is not the absence of force but the presence of friction, without which moving objects retain their speed. Furthermore, without resistance, falling objects accelerate (he observed) at a uniform rate, which he correctly deduced is proportional to the square of the length of time of acceleration.Galileo’s studies of falling objects were rigorous and pioneering investigations which laid the groundwork for our understanding of gravitational force today. They are imperfect in that they do not take into account air resistance or the extremes of shape and size. For example, a feather weighs almost nothing but has a relatively large surface area with which to experience air resistance. From very great heights objects eventually reach a terminal velocity – that is, acceleration no longer increases at Galileo’s uniform rate.But in general his discoveries apply to all compact, dense objects falling from your hands, the Tower of Pisa or any other much taller structure which mankind might have built since. Astronaut David Scott demonstrated the truth of Galileo’s science during the Apollo XV mission, when in the airless atmosphere of the Moon he dropped a feather and a hammer simultaneously and they both hit the moon surface together.Galileo fell foul of the Spanish Inquisition, which in 1633 found him “vehemently suspect of heresy” for his support of heliocentrism. He was forced to “abjure, curse and detest” this truth, and was held under house arrest for the remainder of his life. - eBook - ePub
- John Bird(Author)
- 2019(Publication Date)
- Routledge(Publisher)
section 18.1 :a =v - uta × t = v - u from which v = u + a t- u is the initial velocity in m/s,
- v is the final velocity in m/s,
- a is the constant acceleration in m/s2 and
- t is the time in s.
When symbol a has a negative value, it is called deceleration or retardation. The equation v = u + at is called an equation of motion.Problem 3. A stone is dropped from an aeroplane.Determine (a) its velocity after 2 s and (b) the increase in velocity during the third second, in the absence of all forces except that due to gravityThe stone is free-falling and thus has an acceleration a of approximately 9.8 m/s2 (taking downward motion as positive). From above:final velocity v = u + atfinal velocity v = u + at- (a) The initial downward velocity of the stone u is zero. The acceleration a is 9.8 m/s2 downwards and the time during which the stone is accelerating is 2s. Hence, final velocity, v = u + at = 0 + 9.8 χ 2 = 19.6m/s, i.e. the velocity of the stone after 2 s is approximately 19.6 m/s
- (b) From part (a), the velocity after two seconds u is 19.6 m/s. The velocity after 3 s, applying v = u + at,is v = 19.6 + 9.8 χ 3 = 49 m/s. Thus, the change in velocity during the third second is (49 – 19.6) = 29.4 m/s
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