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Circular motion & pendulum 14 May, 2017 know that change of direction is acceleration know that circular motion is caused by a centripetal force, and the factors that determine the magnitude of the force. Know the meaning of period time, and the effect of length on it. Outcomes C: can name the centripetal force, and state which way it acts. Can explain what periodic time is , and how length alters it. B: can describe why an object travelling at constant speed in a circle is accelerating A: can explain what happens to the size of the force when mass, speed or radius change. Plasticene in a horizontal circle Plasticene in a horizontal circle • Only relevant force is the pull force of the string trying to bring the plasticene into the middle. (Can also be called tension) The object’s velocity is directed along a tangent to the circle Its velocity changes direction as it moves round This change of velocity is towards the centre of the circle. • The amount of force needed increases with the speed of the object. • The amount of force needed increases with the mass of the object. • The tighter the circle the more force is needed. Pendulum Pendulum • It swings because GPE is getting converted into Kinetic as it falls towards the centre. • As it travels through the centre GPE is gained again slowing it down until it stops moving at the maximum height of the swing. • It falls towards centre again. • Friction causes waste energy so it will eventually stop. • The periodic time is the time for one swing and this is constant. • Changing the mass or amplitude does not alter the periodic time. • What else might? Length of string • Investigate if it alters periodic time. •T=1/f • The periodic time is related to 1/ frequency. • 24-25 + 32-34 Hydraulics •Know that pressure in a liquid transmits in all directions. •Know that pressure is force per unit area •Know how a hydraulic machine magnifies force. 14 May, 2017 Outcomes •Explain that liquids transmit force because the molecules are closely spaced. •Use P= F/A •Explain using maths and physics how a hydraulic machine works. Cartesian diver Empty and full lemonade bottle • Why is it so hard to compress the full bottle? Empty and full lemonade bottle • Why is it so hard to compress the full bottle? The force is transmitted between the whole fluidthis is because the particles are so close together and cannot be compressed. Pressure is the spreading out or concentration of force. Drawing pins use this to push into the material. P =F/A, all areas in m2, forces in N, pressure in Pa Syringes • The P=F/A is used here • 30-31 Hydraulic systems Force = xN Force = 10N Y X Area = 0.10m2 Piston X puts pressure on the liquid Area = 0.40m2 How do we calculate the pressure that is being applied from piston X? Hydraulic systems Force = xN Force = 10N f Y X Area = 10cm2 Area = 40cm2 p pressure a = force area Hydraulic systems Force = xN Force = 10N Y X Area = 0.10m2 The pressure stays the same throughout the liquid Area = 0.40m2 What would the pressure be at piston Y? 30-31 Hydraulic systems Force = xN Force = 10N Y X Area = 0.10m2 The pressure stays the same throughout the liquid Area = 0.40m2 What would the Force on piston Y be?