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By Allison Appleby For Physics 2011-12 References: Pearson Aust (2010) In2Physics Shadwick, B (2003) Surfing Physics: Space. Science Press Andriessen et.

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Presentation on theme: "By Allison Appleby For Physics 2011-12 References: Pearson Aust (2010) In2Physics Shadwick, B (2003) Surfing Physics: Space. Science Press Andriessen et."— Presentation transcript:

1 By Allison Appleby For Physics 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

2 Projectile Motion Ideas through time Before Galileo- ideas of Aristotle: horizontal motion and then vertical drop Definition Ballistic Trajectory= the path of an object through the air (subject only to gravity and air resistance)

3 Projectile Motion Ideas through time After Galileo- projectile path is part of a parabola with separate horizontal and vertical components (VECTORS) Horizontal motion is constant velocity Vertical motion is accelerating (g)Definition Ballistic Trajectory= the path of an object through the air (subject only to gravity and air resistance)

4 Projectile Motion Ideas through time When these components are put together we get parabolic motion

5 Projectile Motion Ideas through time The motion of an object depends on the FRAME OF REFERENCE The motion of the object from a viewer at a distance A person running with the object would only see the vertical component of motion

6 Remember from preliminary physics: The motion of a moving object relative to another moving object: v B = v B -v A This is also called the Galilean Transformation Example 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? 20km/hr Click for answer

7 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 a y =g ↑ is the positive direction ↓ is the negative direction As gravity is down a y = m/s 2 Horizontal component is the x axis- velocity is constant a x =0 → is the positive direction ← is the negative direction

8 Properties of ideal parabolic trajectories At maximum height v y =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 90 o launch angle and maximum range is reached at 45 o 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)

9 Solving Projectile Motion Problems We use SUVAT equations from preliminary physics: s = r = displacement = Δx = x f = x i = Δy = y f – y i SOHCAHTOA v=s/t or v av = Δ r / Δ t a av = v-u t SUVAT (straight line motion) Horizontal component Vertical component u x =ucosΘu y =usinΘ v = u + atv x =u x (a x =0)v y =u y + a y t v 2 =u 2 + 2asv x 2 =u x 2 v y 2 =u y 2 + 2a y Δy s= ut + ½ at 2 Δx = u x tΔy = u y t + ½ a y t


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