Gravity

• Gravity is one of the most important forces in the universe
• An object with mass in a gravitational field experiences a force known as weight
• All objects with mass produce a gravitational field
• The more mass an object has, the greater its gravitational field will be
• Weight is the force acting on an object due to gravity, measured in newtons (N) and acts towards the centre of a gravitational field
• Weight is a non-contact force because gravity exerts its force through a field
• Gravitational field strength (g) is measured in newtons per kilogram (N/kg)
• The Earth's gravitational field strength is 9.8 N/kg
• The gravitational field strength of the Moon is 1.6 N/kg
• An astronaut will weigh less on the Moon than they do on the Earth
• Weight caused by gravity is not always obvious
• Astronauts on the International Space Station appear to be weightless because they are constantly falling towards the Earth
• Gravity is one of the most important forces in the universe
• An object with mass in a gravitational field experiences a force known as weight
• Work done = force × distance moved in the direction of the force
• Work is done when energy is transferred from one store to another
• Work is also done when a force causes an object to move
• When work is done against frictional forces acting on an object, the object's temperature increases
• The equation to calculate work done on an object when a force moves it is: work done = force × distance (W = F × s)
• Work done (W) is measured in joules (J)
• Force (F) is measured in newtons (N)
• Gravity is one of the most important forces in the universe
• Distance moved along the line of action of the force (s) is measured in metres (m)
• An object with mass in a gravitational field experiences a force known as weight
• One joule of work is done when a force of 1 N causes a movement of 1 m
• A free body diagram is a simplified drawing of an object or system showing the forces acting on it
• Forces are shown as thin arrows pointing away from the centre of the box or dot representing the object
• Work done can also be measured in newton-metres (Nm): 1 J = 1 Nm
• Free body diagrams do not need to be drawn to scale, but it can be useful if they are
• Example: A doctor weighs 600 N. A lift moves her 40 m to the top floor of a hospital. Calculate the work done on the doctor by the lift
• It is important to label each arrow to show the magnitude of the force it represents
• Examples of free body diagrams include weight and reaction force for a resting object, weight, reaction force, and friction for an object moving at constant speed down a hill, and weight, upthrust, thrust, and air resistance for an accelerating speedboat
• Resolving forces involves breaking down forces acting on an object into their components
• Scalar and vector quantities are important concepts in physics
• Contact and non-contact forces are different types of forces
• Forces and elasticity are related topics in physics
• Describing motion involves understanding the movement of objects
• Gravity is one of the most important forces in the universe
• An object with mass in a gravitational field experiences a force known as weight
• Two forces can be added together to find a resultant force