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Projectile Motion. By Allison Appleby For Physics 2011-12 References: Pearson Aust (2010) In2Physics Shadwick , B (2003) Surfing Physics: Space. Science Press Andriessen et al (2008) Physics 2 HSC course; 3 rd edition. John Wiley and Sons Aus Ltd. Projectile Motion Ideas through time.
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Projectile Motion By Allison Appleby For Physics 2011-12 References: Pearson Aust (2010) In2Physics Shadwick, B (2003) Surfing Physics: Space. Science Press Andriessen et al (2008) Physics 2 HSC course; 3rd edition. John Wiley and Sons Aus Ltd
Projectile Motion Ideas through time Before Galileo- ideas of Aristotle: horizontal motion and then vertical drop Ballistic Trajectory= the path of an object through the air (subject only to gravity and air resistance) Definition
Projectile Motion Ideas through time After Galileo- projectile path is part of a parabola with separate horizontal and vertical components (VECTORS) Ballistic Trajectory= the path of an object through the air (subject only to gravity and air resistance) Vertical motion is accelerating (g) Definition Horizontal motion is constant velocity
Projectile Motion Ideas through time When these components are put together we get parabolic motion
Projectile Motion Ideas through time The motion of an object depends on the FRAME OF REFERENCE A person running with the object would only see the vertical component of motion The motion of the object from a viewer at a distance
Remember from preliminary physics: The motion of a moving object relative to another moving object: vB= vB-vA This is also called the Galilean Transformation Car A is travelling at 100km/hr. Car B is travelling at 80 km/hr in the same direction. What is the velocity of car A compared to car B? Example 20km/hr Click for answer
Ideal parabolic trajectory • Air resistance must be negligible • Height and range of motion is small enough that the curvature of the earth can be ignored • Vertical component is the y axis- acceleration due to gravity ay=g • ↑ is the positive direction • ↓ is the negative direction • As gravity is down ay= -9.8 m/s2 • Horizontal component is the x axis- velocity is constant ax=0 • → is the positive direction • ← is the negative direction
Properties of ideal parabolic trajectories • At maximum height vy=0 • Trajectory is horizontally symmetrical about the maximum height • It takes the same time to reach maximum height as it does to fall back to the original height • Initial speed= final speed (on horizontal ground) • Maximum height is reached at 90o launch angle and maximum range is reached at 45o launch angle • All objects projected horizontally from the same height have the same time of flight as one dropped from rest at the same height (initial vertical velocity = 0)
Solving Projectile Motion Problems We use SUVAT equations from preliminary physics: s = r = displacement = Δx = xf = xi = Δy = yf– yi SOHCAHTOA v=s/t or vav= Δ r/ Δ t aav= v-u t