3. The solar system is held together by gravity

A gravitational field is a field surrounding a massive object, within which any other mass will experience a gravitational force. This force is a force of attraction - the greater the mass, the greater the gravitational attracting force. The gravitational field around a planet has a radial pattern similar to the electric field around a negative point charge. The field lines are in the direction towards the centre of the planet and the closer field lines represent the stronger gravitational field. The presence of another mass (such as a moon) effects the field lines in a way which is similar to the presence of another negative charge. (see Jacaranda p.5 for a diagram) The strength of the gravitational force depends on the mass of the central object, the mass of the object experiencing the force, and on the distance between the two objects. A larger mass of either object increases the gravitational force and increasing the distance decreases the gravitational force. Describe a gravitational field in the region surrounding a massive object in terms of its effects on other masses in it Use available evidence to discuss the factors affecting the strength of the gravitational force

Solve problems and analyse information using Try Jacaranda Chapter 1 Define Newton's Law of Universal Gravitation where F = gravitational force between two objects G = universal gravitational constant = 6.67 x m 1 = mass of object 1 m 2 = mass of object 2 d = distance between the two centres of mass

Newton’s Law of Universal gravitation allows us to calculate the gravitational force experienced by a satellite at any altitude. We understand that this gravitational force is the centripetal force that keeps the satellite in its orbital motion. We can equate the two expressions for force to calculate the orbital velocity of the satellite. We therefore know all quantities (e.g. angular velocity, period etc.) that relate to the uniform circular motion of the satellite. remember r = r E + altitude So high altitude (e.g. geostationary) orbits are lower velocity and low altitude (e.g. low Earth) orbits are higher velocity Discuss the importance of Newton‘s Law of Universal Gravitation in understanding and calculating the motion of satellites

The slingshot effect is a planetary swing-by to pick up speed by gaining K.E. from the planet (which consequently loses a bit of speed) The interaction behaves as an elastic collision ViVi vivi Conservation of momentum and conservation of kinetic energy gives v f = v i + 2V i VfVf N.B. this is the maximum result and will be less if it is not a head-on interaction 10 1 E.g. The satellite (moving at 1 relative to the sun) approaches the planet at a relative velocity of 11 so it will bounce off at a velocity of 11 relative to planet relative to the planet is 21 relative to the sun! Identify that a slingshot effect can be provided by planets for space probes