Forces in Context
Exploring the concept of forces in context, this content covers topics such as resolving forces into i and j components, adding and subtracting forces, finding resultant forces, and using W=mg in problem-solving scenarios. It also delves into the concept of tension, defining it as a force on objects caused by a string pulling them in a given direction with a constant force. Additionally, it discusses weight as a force pulling objects towards the center of the Earth due to gravity. Examples and solutions are provided to aid in comprehension of these fundamental physics principles.
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Presentation Transcript
BAT resolve forces into i and j components BAT add and subtract forces, finding the resultant force in different situations BAT Use W=mg in problems Starter: The balloon is being pushed by resultant force 70 N at an angle of depression of 400 . What are the i and j components of the force ? 70 cos40 = 53.6 70 sin40 = 45.0 400 53.6i 45j 70
Tension What is Tension? Tension is a Force on objects caused by a string pulling them in a direction by a given amount. The string can be a rope or wire. Usually assumed to be inelastic, this means the Force is constant. i.e. the string does not stretch. Tension is usually given by T
WB8 A stone sphere is pulled by two horizontal ropes with Tension and directions shown Suggest a suitable model 10 8 Plan view 400 600 i) The Tension in the ropes is constant the ropes are inelastic ii) No resistant forces iii) The weight is modelled as a particle
WB8 solution A stone sphere is pulled by two horizontal ropes with Tension and directions shown. Find the size of the resultant force in the form xi + yj 10 ?????? ?????? ??????? ??????? 8 400 600 HORIZONTALLY 8cos60 10cos 40= -3.7 VERTICALLY 10sin40+ 8sin 60= 13.6 Resultant force = ?.? = ?.? ? + ??.? ? ??.?
What is weight? Weight is a Force on objects pulling them to the centre of the Earth caused by Gravity The Earth is modelled as a particle which gives objects a constant rate of acceleration g towards the center of the Earth W = mg Weight is given by Where g = 9.8 ms-2 and m is mass (kg)
WB9 A Sign hanging in space with mass 4 kg is pulled by two Cables with Tension and directions shown Suggest a suitable model j j i i i, j notation i, j notation 15 12 500 300 W i) The Weight (W) is constant / g is a constant ii) Cables are inelastic / Tension is constant in each iii) No other forces iv)Sign modelled as a particle
WB9 solution A Sign hanging in space with mass 4 kg is pulled by two Cables with Tension and directions in the same plane as shown Find the resultant force in the form xi+ yj ??????? ??????? ??????? ?? ????? 15 12 500 300 ? ?? W = HORIZONTALLY 15cos50 12cos30= -0.75 VERTICALLY15sin50+ 12sin 30 39.2 = -21.7 ?.?? ??.? Resultant force = - = ?.?? ? ??.? ?
Thrust What is Thrust? When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction on that system. The force applied on a surface in a direction perpendicular or normal to the surface is called thrust For example thrust can be the force caused by a car or plane engine. Or it could be the force exerted by a spring on a ball bearing
WB10 A pinball is at rest on a smooth slope. A spring exerts a thrust of 60 ? on the pinball. Where tan =3 4. Suggest a suitable model i) The Thrust is constant, and acts in a vertical plane ii) Weight (W) is constant / g is a constant iii) No other forces iv)Pinball modelled as a particle v) A smooth slope there are no resistance forces
WB10 A pinball is at rest on a smooth slope. A spring exerts a thrust of 60 ? on the pinball as shown. Where tan =3 Find the resultant force in the form xi+ yj 4. If the pinball has a mass of 0.3 kg ? ? ?? ? tan? =3 sin? =3 cos? =4 4 5 ?0 5 ?.? ??? ? ?.? ??? ? HORIZONTALLY 60 0.3 ??? ?= 59.76 VERTICALLYR = ?.? ??? ? = ?.?? ??.?? ? Resultant force = - = ??.?? ?
WB11 A trailer is being towed by a car up a rough slope, when the car brakes causing a thrust on the tow bar. Suggest a suitable model i) The towbar is inelastic, Thrust is constant, and acts in a vertical plane ii) Weight (W) is constant / g is a constant iii) Trailer modelled as a particle iv)A rough slope the resistance forces are constant and act in a vertical plane
A trailer is being towed by a car up a rough slope of 20 , WB11 when the car brakes causing a thrust on the tow bar of 10 N. The trailer has a mass of 120kg and the resistance force acting on the trailer are 30 N . Find the resultant force in the form xi+ yj ? ? ?? ? ?? ? ??? ??? ?? ??? ??? ?? HORIZONTALLY ?? ?? ?????? ?? = ??.? VERTICALLYR = ??? ??? ?? = ???.? ?? ? Resultant force = = ?? ?
BAT resolve forces into i and j components BAT add and subtract forces, finding the resultant force in different situations BAT Use W=mg in problems self-assess One thing learned is One thing to improve is
